Preheat your oven to 350°F (175°C). This ensures that your bites bake evenly and become perfectly golden.
Lightly grease a muffin tin with cooking spray or line it with muffin liners. This will help prevent the bites from sticking.
In a mixing bowl, combine the cooked quinoa, slightly beaten egg whites, kosher salt, diced red bell peppers, chopped spinach, and shredded mozzarella cheese. Mix well until all ingredients are fully incorporated.
Scoop the quinoa mixture into the prepared muffin tin, filling each cup about three-quarters full. This will allow room for the bites to rise while baking.
Place the muffin tin in the preheated oven and bake for 20-25 minutes, or until the bites are set and lightly golden on top.
Once baked, remove the muffin tin from the oven and let the bites cool for a few minutes. Gently remove them from the tin and serve warm, or allow them to cool completely before storing.