Preheat your oven to 400°F and line a small baking sheet with parchment paper.
Toss the cubed pumpkin with half of the olive oil and roast for 15 minutes until tender and slightly caramelized.
While the pumpkin roasts, heat the remaining olive oil in a 10-inch oven-safe skillet over medium heat and sauté the sliced mushrooms until golden brown.
In a medium mixing bowl, whisk together the whole eggs, liquid egg whites, sea salt, black pepper, garlic powder, and chopped chives until well combined.
Reduce the oven temperature to 350°F and add the roasted pumpkin cubes into the skillet with the mushrooms.
Pour the egg mixture over the vegetables in the skillet, using a spatula to ensure the pumpkin and mushrooms are evenly distributed.
Cook on the stovetop for 2-3 minutes without stirring until the edges are set, then transfer the entire skillet to the oven.
Bake for 12-15 minutes or until the center of the frittata is firm to the touch and the top is lightly golden.