Heat the olive oil and add the leek, red pepper and garlic. Let cook for 2 minutes , making sure not to burn the garlic.
Add the squash and season. Let cook until softened, about 10 minutes.
Meanwhile cook the pasta as per package directions. Reserve 1/2 cup of pasta water.
Once the squash is soft , add the spinach and cook another 5 minutes. Taste and add more salt and pepper to taste. Add the pasta water and parmesan and cook another 5 minutes.