chinese grammar, 做饺子 or 做饭饺子?
The character "饭" itself in the word "做饭" has a literal meaning as "meal". So if you say "做饭饺子", the whole meaning of the sentence would become "prepare 'meal dumplings'", it contains a strange phrase "meal dumplings" (饭饺子) which is not in the regular Chinese vocabulary. 

In this sense, "饭" is just a generic character referred to any kind of meal, if you mean to refer to a specific type of food, you should just replace "饭" with that food such as "饺子".