Preheat your oven to 375°F (190°C) and lightly grease a small oven-safe baking dish with the olive oil.
In a small skillet over medium heat, sauté the diced red bell pepper until it begins to soften, about 3-4 minutes.
Add the baby spinach to the skillet and cook just until wilted, then remove from heat and set aside.
In a medium mixing bowl, whisk together the whole eggs, liquid egg whites, and plain Greek yogurt until the mixture is smooth and well-combined.
Stir in the sea salt, black pepper, and garlic powder into the egg mixture.
Fold the sautéed peppers, wilted spinach, and half of the shredded sharp cheddar cheese into the egg base.
Pour the mixture into the prepared baking dish and sprinkle the remaining cheddar cheese evenly over the top.
Bake for 20-25 minutes, or until the eggs are set in the center and the cheese is bubbly and golden brown.
Allow the casserole to cool for 5 minutes before slicing and serving.