Cook the lentils with 1 teaspoon salt and ½ teaspoon black pepper with 2 cups of water in a medium saucepan over medium-high heat until fully cooked but not mushy, 25 to 30 minutes. Drain lentils of excess water in a fine sieve and let them come to room temperature.

Meanwhile, preheat the oven to 400 degrees F. Heat the olive oil in a large (12-inch) seasoned cast-iron skillet over medium heat. Sauté the onion, stirring frequently, until soft and translucent, about 10 minutes. Add in the garlic and finely diced potato and sauté, stirring often, until the potatoes start to soften a bit, about 15 minutes. Add the spinach and cook, tossing, until wilted but still vibrant green, about 5 minutes. Add the cooked lentils and 1 teaspoon salt and stir.

Whisk the eggs in a large bowl, then mix in the milk, red pepper flakes and half of the feta. Pour over the vegetables in the skillet and gently stir to combine. Then top with the rest of the feta and bake until the eggs are set, 20 to 25 minutes. If desired, turn on the broiler for 3 to 5 minutes to brown the top.

Top with some chopped olives and parsley, tomato slices and a good drizzle of olive oil.