In a small saucepan, bring 1 cup of water to a boil, add the rolled oats, and simmer until creamy and tender.
In a non-stick skillet over medium heat, add 0.5 tsp of the olive oil along with the sliced mushrooms and sauté until golden brown.
Add the fresh spinach to the skillet and cook until just wilted, then remove the vegetables from the pan and set aside.
In a bowl, whisk together the egg whites, whole eggs, sea salt, and black pepper until well combined.
Wipe the skillet clean, add the remaining 0.5 tsp of olive oil, and pour in the egg mixture over medium-low heat.
Once the edges are set, place the sautéed vegetables and crumbled feta cheese on one half of the omelet.
Carefully fold the omelet over the filling and cook for another minute until the cheese is slightly softened.
Serve the fluffy omelet immediately with the warm bowl of oats on the side.