Preheat oven to 400 degrees F. Line a baking sheet with parchment paper and set aside.
Cut the top off the small pumpkin, peel, slice in half, and remove the seeds. Dice the pumpkin into 1" cubes. Transfer to the lined baking sheet and drizzle with 1 tablespoon of the olive oil. Toss with a spatula or your hands and add salt and pepper to taste. Bake for 20-25 minutes or until fork-tender.
In the meantime, core and dice the apples. In a small bowl, whisk together the eggs, milk, cinnamon, salt, and pepper.
When the pumpkin is finished cooking, heat the last 2 tablespoon of olive oil in a 12-inch skillet (cast iron or another oven-safe kind) over medium-high heat. Add the diced apples and cook for 3-4 minutes. Add the pumpkin and use a spoon to spread the pumpkin and apples out evenly in the skillet.
Pour the egg mixture on top. Use your hands (with oven mitts on) to carefully tilt the skillet so that the eggs evenly coat the bottom. Sprinkle the gouda cheese on top. Let the eggs cook for 1-2 minutes, or just until they "set" on the bottom. Transfer the skillet to the oven and bake for 12-15 minutes or until the eggs are cooked through.
Remove from oven, cut into 6 slices, and serve immediately. Enjoy!
Notes
Put the frittata in the oven as soon as the eggs set, and do not overcook. The eggs will continue to cook a little bit in the skillet after you take it out of the oven.
Substitutions/additions: any winter squash for pumpkin, cheddar in place of gouda, and pumpkin pie spice instead of cinnamon.
Serve with a side salad or toast and butter.
Store leftovers in an airtight container in the fridge for 2-3 days. Reheat in the microwave.