Do you have access to whole chickens that has organs inside? You don't have to cook anything. Just crack the eggs open for him to eat it raw, cut up the chickens and feed directly along with the organs, including the bones without cooking it. At 3 months, he can eat chicken necks and wings easily. The chicken backs may be too big for him to chew but you can still try it. Plus all the stuff you're already feeding and leftover scraps from your family's meals. You can also give him some of the fruits you eat. If you have access to other types of meats, you can feed those too - all without any need to cook it. You can cook it, but that's unnecessary. If you do cook, just avoid feeding the bones since it may splinter after it's cooked.
Important is he needs variety of food sources so whatever fresh ingredients you can get will be helpful.