Preheat your oven to 400°F (200°C) and line a large sheet pan with parchment paper.
Slice the chicken sausage into rounds and dice the bell peppers and red onion into bite-sized pieces.
Place the sausage, peppers, and onions on the sheet pan, drizzle with olive oil, and toss to coat evenly.
Spread the mixture into a single layer and roast in the oven for 12 minutes until the vegetables are tender and the sausage is lightly browned.
While the vegetables roast, whisk together the eggs, egg whites, sea salt, black pepper, and garlic powder in a small bowl.
Remove the pan from the oven, pour the egg mixture over the roasted sausage and vegetables, and carefully tilt the pan to ensure the eggs spread evenly.
Return the pan to the oven and bake for another 5 to 7 minutes until the eggs are just set.
Remove from the oven, immediately scatter the baby spinach over the hot eggs, and gently toss with a spatula until the spinach is wilted.