Step 1

Preheat the oven to 400°F.

Step 2

Whisk together the eggs, milk, garlic, salt and pepper until well combined. Set aside.

Step 3

Heat ½ tablespoon olive oil in a 10 or 12-inch cast-iron skillet over medium heat. Add the shallot and cook until translucent, about 5 minutes. Add the leftover roasted squash and spinach. Sauté until the spinach is wilted, then add the egg mixture and gently shake the pan to distribute.

Step 4

Tuck the large chunks of feta into the frittata and transfer back into the oven for 15 to 20 minutes or until the eggs are set. Season to taste and serve with a drizzle of olive oil on top.