Dice the red onion and red bell pepper into small, uniform pieces and slice the chicken sausage into rounds.
Heat the extra virgin olive oil in a medium cast-iron skillet over medium heat.
Add the diced onion and bell pepper to the skillet, sautéing for about 4 minutes until the onions are translucent and the peppers have softened.
Add the sliced chicken sausage to the pan and cook for another 2-3 minutes until the edges are slightly browned and fragrant.
In a small mixing bowl, whisk together the whole eggs and egg whites with the sea salt and black pepper until well combined.
Toss the baby spinach into the skillet and stir for 1 minute until the leaves are just wilted.
Pour the egg mixture over the sausage and vegetables, letting it sit undisturbed for 30 seconds to set the bottom.
Using a spatula, gently fold the eggs from the edges toward the center until they are cooked through but still moist and fluffy.
Remove the skillet from the heat immediately to prevent overcooking and garnish with fresh chopped chives before serving.