Not all food items should be cooked in order for dogs to get the best nutrition possible.
The meat part should be left raw. This is safe for dogs and will give them maximum nutritional benefit. Vegetables and grains should always be cooked because dogs cannot digest raw plant products.
Never boil vegetables. Boiling destroys more nutrients than any other method of cooking. Lightly steam vegetables for maximum nutritional benefit.
Raw meat really is best (all the amino acids and digestive enzymes critical to the health of your dog are left intact and in their most bio-available form this way). If you absolutely must cook the meat, slow cook it at low temperatures for several hours. The less heat you use, the more nutrients remain.
Variety is also key. Your dog will suffer nutritional deficiencies if you feed the same meal every day long term. Rotate meats (beef, chicken, lamb, turkey, duck, fish, rabbit, pork) on a weekly basis. Also rotate the vegetables and carbs. Use sweet potatoes one week, rice the next, oatmeal the next, etc. The more variety, the better. Home made diets should be about 50% meat, 25% veggie/fruit, and 25% carbohydrate (sweet potatoes count as a carb, not a veggie).
You can always include a vitamin powder like Missing Link if you are still concerned about proper nutrients.