Preheat oven to 375 degrees F (190 degrees C).
Dice the Onion (to taste).
Dice the Bell Pepper (to taste).
Dice the Ham (to taste).
In a frying pan, cook up the onions, bell peppers and ham.
Grate the Cheese (to taste) if not using pre-grated.
Grease a 6 spot muffin tin. Fill each muffin cup with cooked omelet ingredients. Top with cheese.
Mix Egg (4), Milk (1/4 cup), Baking Powder (1/2 teaspoon), Oil (1/2 teaspoon), Salt and Pepper (to taste) in a bowl. Pour egg mixture in each muffin cup. You should fill each about 4/5 of the way to the top.
Put in oven and bake for 20-25 minutes.
Take out of oven and let rest for 5 minutes before serving or storing. Enjoy!