Δεν μου αρέσει πολύ το κέτσαπ, αλλά το ζαμπόν στο τοστ είναι νόστιμο.

Because Greek expresses this idea as something is pleasing to someone.

So:

• μου = to me
• αρέσει = pleases / is pleasing

A very literal version of Δεν μου αρέσει πολύ το κέτσαπ would be:

Ketchup does not please me very much.

That is the normal Greek way to say I don’t like ketchup very much.

Because the thing being liked is το κέτσαπ, which is singular.

With αρέσει / αρέσουν, the verb agrees with the thing that is pleasing:

• Μου αρέσει το κέτσαπ. = I like ketchup.
• Μου αρέσουν οι πατάτες. = I like potatoes.

So here:

• το κέτσαπ = singular
• therefore αρέσει = singular

μου is the weak pronoun form meaning to me.

It comes from the first-person pronoun and functions like an indirect object. In older grammar terms, this is a genitive form, but in meaning it often corresponds to English to me.

Some related forms are:

• μου = to me
• σου = to you
• του / της = to him / her
• μας = to us
• σας = to you (plural or polite)
• τους = to them

So μου αρέσει is literally it pleases me.

δεν is the standard negation particle for statements.

So:

• Μου αρέσει το κέτσαπ. = I like ketchup.
• Δεν μου αρέσει το κέτσαπ. = I do not like ketchup.

In Greek, δεν normally goes before the verb phrase, so δεν μου αρέσει is the natural order.

Here πολύ means very much / a lot.

So:

• Μου αρέσει πολύ = I like it very much
• Δεν μου αρέσει πολύ = I don’t like it very much

In this sentence, πολύ modifies the whole idea of liking, not the ketchup itself.

This placement is very natural in Greek:

• Δεν μου αρέσει πολύ το κέτσαπ.

It gives the softer meaning I don’t like ketchup very much, rather than a stronger I hate ketchup.

Because all three nouns are treated here as neuter singular nouns, so they take the article το.

Also, Greek uses the definite article much more often than English. Even when English says just ketchup or ham, Greek often says:

• το κέτσαπ
• το ζαμπόν
• το τοστ

This is completely normal.

So Greek often uses the article where English would not:

• Μου αρέσει ο καφές. = I like coffee.
• Δεν τρώω το βράδυ. = I don’t eat at night.
  (Different structure, but it shows Greek article/use patterns are not the same as English.)

στο is a contraction of σε + το.

So:

• σε το → στο

Literally, στο τοστ means in/on the toast.

But there is an important vocabulary point: in everyday Greek, τοστ often means a toasted sandwich / toastie, not just a plain slice of toast.

So το ζαμπόν στο τοστ is most naturally understood as:

the ham in the toasted sandwich

That is why this sounds natural in Greek.

Because the adjective must agree with the noun it describes.

Here the noun is:

• το ζαμπόν = neuter singular

So the adjective is also neuter singular:

• νόστιμο

Compare:

• ο καφές είναι νόστιμος = the coffee is tasty
• η σούπα είναι νόστιμη = the soup is tasty
• το ζαμπόν είναι νόστιμο = the ham is tasty

In the sentence, στο τοστ is just extra information telling you where the ham is. The adjective still agrees with το ζαμπόν.

Yes.

The whole noun phrase το ζαμπόν στο τοστ is the subject, and είναι νόστιμο says something about it.

So the structure is:

• το ζαμπόν στο τοστ = the ham in the toasted sandwich
• είναι νόστιμο = is tasty

Greek does not need a separate word for it here, because the subject is already clearly stated.

Yes, Greek word order is more flexible than English, although the version you have is the most neutral and natural.

For example:

• Δεν μου αρέσει πολύ το κέτσαπ = neutral
• Το κέτσαπ δεν μου αρέσει πολύ = puts more focus on ketchup
• Νόστιμο είναι το ζαμπόν στο τοστ = puts more emphasis on tasty

So the original sentence is a good standard model, but other orders are possible for emphasis.

Yes, all three are borrowed words.

• κέτσαπ comes from ketchup
• ζαμπόν comes from French jambon
• τοστ comes from toast

In Modern Greek, words like these are often treated as neuter and are commonly used with the article το.

That helps explain why they may not look like older, more traditional Greek noun patterns.