Preheat the oven to 425 degrees.

Heat the oil in a 10" oven-safe skillet over medium-high heat. Once oil is shimmering, add in the leeks and carrot noodles, season with salt and pepper and cook until leeks are softened, about 5 minutes. Add in the garlic and stir until fragrant, about 30 seconds. Pour over the eggs and add the feta cheese, pressing the cheese into the eggs. Let the frittata cook until the bottom is set and then transfer to the oven and cook for 10-15 minutes or until eggs fully set.