Preheat oven to 350 degrees F. Grease muffin tins using butter or cooking spray, making sure to cover the sides and bottom of each cup.
Cut bread into circles using a cookie cutter. Use a rolling pin to flatten the bread slices.
Place 1 bread circle in each muffin tin cup. Bake for 2-3 minutes to dry out the bread slightly. Meanwhile, prepare the rest of your ingredients.
Remove muffin tins from oven. Add desired toppings (peppers, meat, etc.) to each bread cup.
Whisk together the eggs and milk. Add salt and pepper to taste. Pour some of the egg mixture into each tin, dividing evenly.
Sprinkle some shredded cheddar cheese on top of each cup.
Bake at 350 degrees F for about 20 minutes, or until the egg is cooked through.
Allow to cool for 1 minute. Remove omelets from pan by running a knife around the edges, then gently lifting them out. Serve warm.
Advanced preparation tip: store cooked omelets in the freezer, then microwave for a couple of minutes for a quick breakfast.