Pre-heat your oven to 350.
Bring the oil to medium heat in an 8”-10” oven-safe nonstick skillet over medium heat. Add the cubed butternut squash and stir to coat. Sprinkle with a bit of salt and pepper to taste. Cook, stirring regularly, for 6 minutes. Add the chopped prosciutto and stir together. Continue to cook for an additional 2 minutes. Add the chopped spinach and stir. Cook for 2 more minutes, stirring a few times, until the squash is softened and a bit browned and the spinach is wilted.
While the squash is cooking, break the eggs into a large mixing bowl and whisk together until just combined. Add the yogurt, salt, black pepper, sage, thyme and shredded parmesan and stir together until mixed.
When the squash, prosciutto and spinach are cooked, transfer them into the bowl containing the egg mixture and stir together. Spray the skillet you used liberally with cooking spray and then pour the egg mixture into the skillet. Cook on a burner set to medium heat for 5-7 minutes until the very outside edge of the frittata starts to turn opaque/look cooked. Transfer the skillet into the oven and cook for 15-17 minutes until the center is set. Let cool for 5 minutes, then slice into 6 slices and serve.