Preheat oven to 350 F, and prep the top rack so it's in the center of your oven. Place a 12 cup muffin pan on a rimmed baking sheet, and spray the muffin pan generously with cooking spray.
Add egg whites, cream cheese, cheese, salt, and pepper to a blender, and blend until smooth.
Divide the spinach and roasted peppers into the 12 cups of the muffin pan, then pour the egg whites on top.
Place the baking sheet and muffin pan into the oven, and pour water into the baking sheet so it's about halfway full.
Bake until the egg bites are completely set in the center, about 30 minutes. Allow them to cool for a few minutes before removing, if they're hard to remove, use a spoon to trace the edges. Enjoy!
Notes
Mix-ins - feel free to use whatever mix-ins you prefer, just be sure they're grates, or finely chopped! Also, don't use watery veggies. If using something packed in liquid, I like to gently ring out the liquid with towels (added water may prevent the bites from setting).
Preventing watery egg bites - the best way to do this is to loosely tent the mold with aluminum foil (I'm talking just place a sheet on top).
How to make oven baked egg bites -
Prepare the oven racks so that the top rack is in the middle, and the bottom rack is a few inches below that. Preheat the oven to 350 F, and coat a muffin tin pan generously with cooking spray.
Place a 9x13 casserole dish on the bottom rack, and pour about 1" of boiling water into it.
(Follow steps above for making the egg bite filling)
Place the muffin tin pan on the top rack, and bake for 25-27 minutes, until the egg bites have completely set.