1) Preheat oven to 350 degrees F. Whisk together eggs, milk, a pinch of kosher salt and pepper.
2) If you have roasted peppers already, just roughly chop them along with leeks. When preparing the leeks, cut off the root end and cut the leek into quarters. Then rinse it will to remove dirt and chop it up.
If you need to roast your peppers, you an do so on a high grill, over a gas stove top range, or in a 500 degree oven until they are blistered and black. Then let the peppers steam in a covered bowl for 10 minutes and peel them.
3) Add a drizzle of oil to a cast iron skillet over medium heat. Once hot, add the leeks and chiles and cook for a few minutes until veggies soften. Add garlic and season with salt and pepper. Continue to cook for a minute.
4) Distribute the veggies evenly over the cast iron skillet and pour in egg mixture. Cook on the stove top for 3-4 minutes until eggs start to set on the bottom (they will still be uncooked on top).
5) Add grated cheese to frittata and move to oven. Bake for 6-8 minutes until eggs are puffed and cheese is melted.
6) When frittata comes out, slice it into quarters and serve it with extra chiles on top.