Preheat your oven to 375°F (190°C) and lightly grease a small baking dish with a touch of olive oil.
Place a non-stick skillet over medium heat with the olive oil, then add the diced red onion, bell pepper, and mushrooms.
Sauté the vegetables for 5-6 minutes until they are tender and the moisture from the mushrooms has mostly evaporated.
Add the baby spinach to the skillet and toss for 1 minute until just wilted, then remove the pan from heat to cool slightly.
In a medium mixing bowl, whisk together the liquid egg whites, low-fat cottage cheese, sea salt, black pepper, and garlic powder until well combined.
Stir the sautéed vegetable mixture into the egg white base, then pour the entire mixture into the prepared baking dish.
Sprinkle the crumbled feta cheese evenly over the top of the egg mixture.
Bake for 25-30 minutes, or until the center is set and the edges are slightly golden and pulling away from the sides.
Allow the bake to rest for 5 minutes before slicing and serving.