Step 1: Preheat your oven to 400°F (200°C). Toss the cubed pumpkin with 1 tablespoon of olive oil and a pinch of salt. Spread on a baking sheet and roast for 15-20 minutes or until tender.
Step 2: While pumpkin roasts, lower oven temperature to 375°F (190°C). Heat the remaining olive oil in a 10-inch oven-safe skillet over medium heat.
Step 3: Add the sliced mushrooms to the skillet and cook for 5-7 minutes until they are golden brown and their moisture has evaporated.
Step 4: Stir in the minced garlic and fresh spinach. Sauté for 1-2 minutes until the spinach is wilted. Remove from heat briefly.
Step 5: In a large bowl, whisk together the eggs, heavy cream, nutmeg, salt, and pepper until well combined but not excessively frothy.
Step 6: Spread the roasted pumpkin cubes evenly in the skillet with the mushrooms and spinach. Pour the egg mixture over the vegetables.
Step 7: Sprinkle the crumbled feta or goat cheese over the top. Place the skillet back on medium heat for 3-5 minutes to let the bottom set.
Step 8: Transfer the skillet to the oven and bake for 12-15 minutes, or until the center of the pumpkin mushroom and spinach frittata is just set and the top is slightly golden.
Step 9: Remove from the oven, let it rest for 5 minutes, garnish with fresh parsley, and slice into wedges.