Preheat your oven to 375°F (190°C). Begin by chopping the leafy greens and set them aside. Measure out the sliced squash, diced sweet potatoes, and beaten eggs. Warm the olive oil in an oven-safe skillet over medium heat, then add the sweet potatoes and cook until slightly crispy, about 5 minutes.
Add the sliced squash to the skillet and sauté for another 3-4 minutes until tender. Sprinkle in the cinnamon and nutmeg, stirring to coat the vegetables evenly and let the aromas develop. Toss in the leafy greens and cook until wilted, about 2 minutes.
Spread the vegetable mixture evenly in the skillet, then pour the beaten eggs over the top. Tilt the pan gently to distribute the eggs throughout the vegetables. Season with salt and pepper to taste.
Transfer the skillet into the preheated oven and bake for 20-25 minutes, until the eggs are puffed and just set, with a lightly golden surface.
Remove the skillet from the oven and let the frittata rest for a few minutes. Slice into wedges and serve warm, enjoying the vibrant colors and hearty textures.