Preheat oven to 375 degrees. Coat a 12 cup muffin tin with non-stick spray.

If using bacon, cook, drain and break into bits.

Place the eggs in a large bowl and add baking powder, salt and pepper. Whisk well to combine.

Layer the cheese, scallions, bell pepper, mushrooms and bacon or ham into the bottom of the prepared muffin tins.

Pour the egg mixture into the cups until about 3/4 full.

Bake for 15 to 20 minutes, until the egg muffins rise and the edges are slightly browned. Serve immediately.

Baked egg muffins can be frozen and reheated. Let the cooked muffins cool completely. Then wrap each egg muffin in a piece of wax paper, transfer them to a large Ziploc bag and freeze for up to one month. To reheat in the microwave, wrap in a paper towel and heat on 80% power for about 2 minutes. To reheat in the oven, preheat the oven to 200 degrees. Warm the muffins for 10 minutes or until heated through.