Preheat your oven to 375°F (190°C) and line a large rimmed sheet pan with parchment paper.
Place the chopped bell peppers and zucchini on the sheet pan and drizzle with avocado oil.
Season the vegetables with sea salt, black pepper, and garlic powder, then toss to coat evenly.
Spread the vegetables into a single layer and roast in the oven for 12 minutes until they begin to soften.
While the vegetables are roasting, whisk together the whole eggs and liquid egg whites in a medium bowl until well combined.
Remove the sheet pan from the oven and scatter the fresh baby spinach evenly over the roasted vegetables.
Carefully pour the egg mixture over the vegetables, tilting the pan slightly if needed to ensure the eggs reach all corners.
Sprinkle the crumbled feta cheese across the top of the egg and vegetable mixture.
Return the pan to the oven and bake for another 12 to 15 minutes, or until the eggs are completely set and the edges are lightly golden.
Allow the sheet pan to cool for a few minutes before slicing into squares and serving warm.