Preheat the oven to 375°F and spray a muffin tin with olive oil spray.
Cut crusts of sliced bread, then roll them out with a rolling pin until they’re flattened and thin. Lightly spray both sides of bread with olive oil. Cut each bread slice in half diagonally.
With cut sides facing, place 2 bread halves in each of 6 muffin cups, making sure to cover bottom entirely and allowing bread corners to extend above rims.
Place cheese in the bottom of each bread crevice along with onions and peppers, if desired. Then, carefully crack an egg on top. Season with salt and pepper and bake in the preheated oven until the egg whites are set, and not jiggly, about 15-18 minutes.
Remove the baked eggs from the muffin tin and garnish with fresh parsley, if desired.