Cook the spaghetti squash using one of the methods below until desired tenderness is reached.

Pressure Cooker Method: Place the spaghetti squash and 1 cup of water in the pressure cooking pot. You can keep them whole or cut them in half lengthwise (sometimes they fit better that way). You don't need to remove the seeds before cooking but you can if you'd like (I usually don't). Make sure that the squash will not block the lid from sealing and then lock the lid in place. Cook 7-10 minutes on high pressure, depending on your desired "doneness". We like ours fairly tender. Use a quick pressure release and carefully open cooker.

Oven Method: Cut the squash in half and place cut side down on a lightly greased baking sheet (no water needed). Bake at 375 degrees for 40-50 minutes until it is very tender. 

Microwave Method: Cut squash in half lengthwise. Place cut sides up on a microwave safe plate and cover with cling wrap. Microwave on high for 8-10 minutes or until tender. Allow to cool enough to handle before unwrapping.

Preheat oven to 400 degrees F.

Prepare the sauce in a large 12-inch nonstick skillet over medium heat. Heat the olive oil until hot, then add onions and garlic and cook for about 3 minutes until onions start to soften. Add Italian sausage and cook, breaking it up into small pieces as it cooks until meat is no longer pink. Stir in the diced tomatoes and basil and simmer for about 5 minutes until sauce begins to thicken.

Prepare cheesy topping by combining ricotta, fresh Parmesan, parsley, ¼ teaspoon salt and ⅛ teaspoon pepper in small bowl. Stir in ½ cup mozzarella cheese into the topping, reserving ¼ cup for later.

Scoop out the seed layer of spaghetti squash and discard. Drain excess liquid from spaghetti squash and scoop into a large bowl. Reserve the shells, if using for serving (optional).

Toss the spaghetti squash with ½ teaspoon salt, ¼ teaspoon black pepper, and ½ of the prepared sauce. Divide evenly and place back into the reserved shells on a baking sheet OR place in an greased 8x8-inch square baking pan.

Top spaghetti squash with ricotta cheese mixture (dividing evenly between shells, if using) and sprinkle with ¼ cup grated mozzarella cheese.

Bake in preheated 400 degree F for 20 minutes or until spaghetti squash is heated through and cheese is lightly brown and bubbly. Garnish with chopped fresh basil or parsley, if desired.