@shalom4me: it's just saying the cook doesn't work in a short-order joint. He works in a real full-service restaurant.
A cook can be serious, but I have never heard of a serious restaurant! This seems to have lost someting in translation.
How to you know if it's "the restaurant" or "a restaurant" if there's a preposition attached?
It's written the same but pronounced differently: beh-mis'adah (in a restaurant), bah-mis'adah (in the restaurant)
According to the audio, it says here bemisadah and not bamisadah, which means that there is no definite article here (ב+ה creates ב which is pronounced as ba instead of be)
If it was "at THE serious restaurant" it would say "בסעדה הרצינית". Here it just says "במסעדה רצינית", meaning at A serious restaurant. Make sense?