If using frozen butternut squash, thaw by running under hot water. Preheat the oven to 400°F. Toss the butternut squash cubes with about 1 ½ teaspoon of the olive oil, ½ teaspoon sea salt and pepper. Roast until the squash is tender, about 20 minutes.
Whisk together the eggs, milk, and garlic and set aside.
Heat the ghee or coconut oil in an 8-inch cast-iron skillet over medium heat. Add the leeks and saute until soft, about 1 minute.
Stir in the herbs and roasted butternut squash and cook for another minute. Add the egg mixture and spread in an even layer. Transfer the skillet to the oven and bake for 20 to 25 minutes, or until the eggs are set and the edges are golden brown.