Preheat your oven to 375°F (190°C) and line a small rimmed sheet pan with parchment paper for easy cleanup.
Dice the red bell pepper, zucchini, and red onion into small, uniform pieces to ensure even roasting.
Place the diced vegetables on the sheet pan, drizzle with olive oil, and sprinkle with sea salt, black pepper, and garlic powder.
Toss the vegetables to coat and roast in the oven for 10 minutes until they begin to soften and develop color.
While the vegetables roast, whisk the whole eggs and liquid egg whites together in a medium bowl until the mixture is smooth and frothy.
Remove the pan from the oven and scatter the baby spinach evenly over the roasted vegetables.
Carefully pour the egg mixture over the vegetables and spinach, ensuring it reaches all corners of the pan.
Top the eggs with the crumbled feta cheese and return the pan to the oven.
Bake for 12-15 minutes, or until the eggs are completely set in the center and the edges are lightly golden.
Allow the sheet pan to cool for a minute before slicing the eggs into squares and serving.