Combine the chopped bell peppers and spinach in a mixing bowl.
Add the non-salt seasoning and toss the vegetables until they are well coated.
Spray a 12-cup muffin pan thoroughly with nonstick cooking spray.
Distribute the veggie mixture evenly among the muffin cups and sprinkle each with shredded cheddar cheese.
Pour the egg whites carefully over the veggies and cheese in each cup and sprinkle a little sea salt on top.
Place the pan in a preheated oven at 350°F and bake for 15 to 17 minutes, or until the muffins are firm and lightly browned.