01 - Preheat oven to 375°F.
02 - Heat olive oil in a 10-inch oven-safe skillet over medium heat. Add diced red onion and red bell pepper; sauté for 3–4 minutes until softened.
03 - Stir in minced garlic and cook for 1 minute. Add chopped spinach and cook for another 1–2 minutes until wilted.
04 - Add cooked lentils to the skillet and mix until evenly combined with the vegetables.
05 - In a large bowl, whisk together eggs, milk, dried oregano, salt, and black pepper. Stir in half the chopped fresh parsley.
06 - Pour the egg mixture evenly over the vegetables and lentils in the skillet. Gently shake or stir to distribute ingredients evenly.
07 - Sprinkle crumbled feta cheese evenly across the top of the mixture.
08 - Cook on the stovetop over low heat for 2–3 minutes until the edges begin to set.
09 - Transfer the skillet to the preheated oven and bake for 12–15 minutes, or until the center is set and the top is lightly golden.
10 - Remove from the oven and let cool slightly. Garnish with remaining fresh parsley. Slice into wedges and serve warm or at room temperature.