Preheat your oven to 375°F and line a large rimmed sheet pan with parchment paper for easy cleanup.
Finely dice the red and green bell peppers and the red onion, and slice the chicken sausage into thin rounds.
Place the diced peppers, onion, and sausage on the sheet pan, drizzle with olive oil, and toss to coat evenly.
Roast the vegetables and sausage in the oven for 10 minutes until they begin to soften and the sausage is slightly browned.
While the vegetables roast, whisk the whole eggs, egg whites, sea salt, black pepper, and garlic powder in a medium bowl until fully combined.
Remove the pan from the oven, scatter the baby spinach over the hot vegetables, and pour the egg mixture carefully over everything.
Return the sheet pan to the oven and bake for 12 to 15 minutes, or until the eggs are set and the edges are golden.
Allow the sheet pan to cool for a few minutes before slicing the eggs into squares and serving warm.