Spray skillet with cooking spray and heat over medium-high. Dice pepper, onion, and mushrooms; add to skillet. Sauté for 2-3 minutes.
Whisk eggs and egg whites together, add to skillet. Cook for 2-3 minutes without stirring to allow eggs to set slightly. Stir eggs to begin scrambling. Cook until no longer runny. For larger curds of eggs, only stir occasionally.
Remove skillet from heat. Add spinach and cover skillet to allow spinach to wilt. Meanwhile, cut melon into chunks and toast bread.