Combine lentils and bay leaf in a sauce pan. Cover with plenty of water and bring to a boil. Simmer for 12-15 minutes, or until tender.
Meanwhile, cut the spaghetti squash in half and scoop out the seeds. Place face down on a large plate with 1 TBS water. Microwave on high for 5 minutes, or until just tender enough to scrape out the strands.
Combine scraped spaghetti squash strands with cooked lentils (bay leaf removed), basil, Parmesan, balsamic, salt and pepper. Stir until well combined.
Place the spaghetti squash mixture back into the spaghetti squash shells. Top with mozzarella and broil on high for 2 minutes, or until the just is melted and just starting to brown.
Recipe by Alison's Allspice at https://www.alisonsallspice.com/lentil-marinara-spaghetti-squash-boats/