Preheat oven to 375 degrees.
Cut squash into two-inch rounds and remove the seeds.
Sprinkle with salt and bake for an hour, flipping over after 30 minutes.
Cut the zucchini, chop the onions and mince the garlic.
In a large skillet, sauté the onions, zucchini and garlic in 1 tablespoon oil for 5 minutes.
Add the sausage and cook until browned and cooked through.
Shred the Parmesan & mozzarella cheeses.
Add the marinara sauce and cook down for 15 minutes on low.
Cool the squash to room temperature.
Using a fork shred the squash into spaghetti noodles.
Place the squash in a colander and cover with a clean, dry dishtowel, pressing down to squeeze out excess moisture.
In a bowl and add the ricotta, eggs salt and pepper and mix together.
Add the squash to the egg and ricotta, stirring to fully combine.
Coat a 9-inch casserole dish with olive oil and spread the squash and ricotta mixture evenly over the bottom of the dish.
Pour the mariner sauce over the squash.
Sprinkle with the cheeses.
Bake for 30 minutes or until bubbly, let rest a few moments and serve.