Preheat the oven to 400'.
Halve the squash, scoop out the seeds, rub with oil, and roast cut side down for 45 minutes.
Let cool, shred the squash, and reserve shells.
Saute onions, garlic, and spinach in a skillet.
Mix spinach with ricotta, herbs, mozzarella, parmesan, and lemon juice.
Fill squash shells with marinara, meat (if using), and squash mixture.
Top with mozzarella and parmesan, bake for 20 minutes, then broil to brown tops.
Garnish with fresh parsley and serve warm.
