Pieczony kurczak jest pyszny.

Because pieczony has to agree with kurczak in gender, number, and case.

• kurczak is masculine singular
• the sentence uses the nominative case, because pieczony kurczak is the subject
• so the adjective/participle must also be masculine singular nominative: pieczony

Compare:

• pieczony kurczak = roasted chicken
• pieczona ryba = roasted fish
• pieczone mięso = roasted meat

Pieczony is a form derived from the verb piec = to bake / to roast. In this sentence, it works like an adjective and means roasted or baked.

So pieczony kurczak literally means roasted chicken.

English learners often think of it as a past participle, and that is a useful way to understand it. In normal Polish usage here, though, it simply behaves like an adjective describing the chicken.

Because pyszny is an adjective, and it describes the noun kurczak.

• pyszny = delicious, tasty
• pysznie = deliciously, tastily

In Pieczony kurczak jest pyszny, the structure is:

• Pieczony kurczak = subject
• jest = is
• pyszny = adjective describing the subject

So Polish uses the adjective form, just like English uses delicious, not deliciously.

All the descriptive words here are in the nominative singular masculine form.

• pieczony kurczak is the subject, so it is in the nominative
• pyszny also appears in the nominative because it is a predicate adjective after jest

So the sentence is built very simply:

• Pieczony — nominative masculine singular
• kurczak — nominative masculine singular
• jest — 3rd person singular of być (to be)
• pyszny — nominative masculine singular

In standard Polish, no. You normally need jest here.

• Pieczony kurczak jest pyszny = correct
• Pieczony kurczak pyszny = not standard as a normal sentence

Polish often omits subject pronouns like on, ona, ja, but it does not usually omit the verb to be in this kind of present-tense sentence.

The most natural neutral order is:

Pieczony kurczak jest pyszny.

Polish word order is more flexible than English, so other orders are possible, but they may sound marked, poetic, or emphasize something different.

For example:

• Kurczak pieczony jest pyszny — possible, but less neutral
• Pyszny jest pieczony kurczak — puts extra focus on pyszny

For a learner, the original word order is the best default.

It can mean either, depending on context.

• kurczak can mean a chicken as an animal
• it can also mean chicken as food

In this sentence, because of pieczony and pyszny, it clearly means the food: roasted chicken.

Because Polish has no articles.

English distinguishes between:

• a roasted chicken
• the roasted chicken
• sometimes just roasted chicken

Polish simply says:

• pieczony kurczak

The exact meaning depends on context. So this sentence could mean:

• Roasted chicken is delicious
• The roasted chicken is delicious
• A roasted chicken is delicious

In real use, the situation tells you which meaning is intended.

A rough English-friendly approximation is:

pye-CHO-nih KOOR-chak yest PISH-nih

A few useful sound notes:

• pie sounds roughly like pye
• cz sounds like ch in church
• kur has a clear oo sound
• jest sounds close to yest
• sz sounds like sh
• Polish y is not exactly English ee or i; it is a harder central vowel, but ih is a helpful approximation

If you want to sound more natural, stress is usually on the second-to-last syllable of each word:

• pieCZOny
• kurCZAK
• JEST
• PYSZny

Here are the basic dictionary forms:

• pieczony → from piec = to bake / roast
• kurczak = chicken
• jest → from być = to be
• pyszny = delicious

So a learner could break the sentence down as:

• piec → pieczony = roasted
• kurczak = chicken
• być → jest = is
• pyszny = delicious

Yes. Smaczny is also correct, but the tone is a little different.

• smaczny = tasty
• pyszny = delicious, very tasty

So:

• Pieczony kurczak jest smaczny = Roasted chicken is tasty.
• Pieczony kurczak jest pyszny = Roasted chicken is delicious.

Pyszny sounds a bit stronger and more enthusiastic.

Because it agrees with the thing being described: kurczak.

Even though pyszny comes after jest, it still matches:

• kurczak — masculine singular
• so pyszny — masculine singular

Compare:

• Kurczak jest pyszny = The chicken is delicious.
• Ryba jest pyszna = The fish is delicious.
• Mięso jest pyszne = The meat is delicious.

So the ending changes because the noun changes.

Yes, it is completely natural and standard.

It is a simple everyday sentence with a very common pattern:

[adjective + noun] + jest + [adjective]

For example:

• Gorąca kawa jest dobra. = Hot coffee is good.
• Świeży chleb jest pyszny. = Fresh bread is delicious.
• Pieczony kurczak jest pyszny. = Roasted chicken is delicious.

So this is a very useful model sentence for learners.