Preheat your oven to 375°F (190°C) and line a small rimmed sheet pan with parchment paper or grease lightly with olive oil.
Place the diced bell peppers and red onions on the sheet pan, drizzle with olive oil, and toss to coat evenly.
Roast the vegetables for 10 minutes until they begin to soften and develop a slight char.
While the vegetables roast, whisk together the whole eggs, liquid egg whites, sea salt, black pepper, and garlic powder in a large bowl until the mixture is uniform.
Remove the pan from the oven, stir in the chopped baby spinach, and spread the vegetable mixture into an even layer across the pan.
Carefully pour the egg mixture over the vegetables, ensuring it reaches all corners of the pan without overflowing.
Bake for an additional 12-15 minutes, or until the eggs are fully set in the center and the edges are slightly golden.
Allow the sheet pan to cool for 5 minutes before slicing the eggs into large squares for serving.