Learn Hardcore Japanese: kono mise ha teisyoku ga yasukute oisii node, hiru ha itumo konzatusite imasu. - This place has cheap and tasty set meals, so it is always crowded at lunchtime.

この　店みせ　は　定食ていしょく　が　安やすくて　おいしい　ので、　昼ひる　は　いつも　混雑こんざつして　います。kono mise wa teishoku ga yasukute oishii node, hiru wa itsumo konzatsushite imasu.

This place has cheap and tasty set meals, so it is always crowded at lunchtime.

Breakdown of kono mise wa teishoku ga yasukute oishii node, hiru wa itsumo konzatsushite imasu.

Questions & Answers about kono mise wa teishoku ga yasukute oishii node, hiru wa itsumo konzatsushite imasu.

Why are there two topic/subject markers here: 店は and 定食が?

They are doing different jobs.

この店は sets the overall topic: as for this restaurant...
定食が marks what is being described within that topic: the set meals are cheap and delicious.

So the structure is roughly:

As for this restaurant, its set meals are cheap and tasty, so...

This is very common in Japanese: one thing is the big topic, and another thing inside that topic gets marked with が as the subject of a description.

Why is it 定食が安くておいしい and not 定食は安くておいしい?

You could say 定食は in some contexts, but 定食が is more natural here because it presents the set meals as the thing that has the qualities cheap and delicious.

A useful way to think about it:

が: identifies what has the property
は: introduces or contrasts a topic

Here, the sentence is already about この店は, so using 定食が fits well:
As for this restaurant, the set meals are cheap and delicious...

If you used 定食は, it might sound more contrastive, like as for the set meals...

Why is 安い changed to ?