To cook a meal for dinner or to cook the meal for dinner in the sentence like " I cooked the meal for dinner yesterday."? Which one is proper English?
Proper everyday English (one p) would just be "To cook dinner". Dinner is a meal there's redundancy in either of your options.
You could just about use the first in some situations: "We were only going to have leftovers but in the end I cooked a meal for dinner yesterday". It doesn't sound quite natural even then -- I'd probably be more specific ("...in the end I cooked pizza...") or rephrase slightly: "We were only going to have leftovers but in the end I cooked a proper dinner yesterday".