Preheat your oven to 375°F and line a 9x13 inch rimmed sheet pan with parchment paper for easy cleanup.
Dice the red bell pepper and halve the cherry tomatoes, then spread them onto the prepared sheet pan.
Drizzle the vegetables with olive oil and sprinkle with sea salt, tossing to coat evenly.
Roast the vegetables in the oven for 10 minutes until they begin to soften and release their juices.
While the vegetables roast, whisk together the whole eggs, egg whites, black pepper, and garlic powder in a medium bowl until well combined.
Remove the pan from the oven and scatter the chopped baby spinach over the hot roasted vegetables.
Pour the egg mixture carefully over the vegetables, ensuring it spreads to all corners of the pan.
Sprinkle the crumbled feta cheese over the top and return the pan to the oven.
Bake for 12 to 15 minutes or until the eggs are completely set in the center and slightly golden on the edges.
Allow the eggs to cool for a few minutes before slicing into squares and serving warm.