For the oven baked omelet: Heat the 2 remaining tablespoons of olive oil in cast iron or oven safe skillet over medium high heat. Add onions and tomatoes and sauté for 4 minutes. Add fresh spinach and continue to sauté until wilted. Season with salt and pepper, add roasted butternut squash and stir to combine. Stir in whisked eggs, reduce heat to simmer and cook undisturbed for 2 minutes or until bottom is set. Transfer the pan to the oven and cook for 15-20 minutes or until eggs are set. Remove from oven, allow to cool for 5 minutes, run knife around edges to loosen. Slice and serve warm garnished with additional sage leaves.