Preheat oven to 400 degrees F. Prepare the spaghetti squash by slicing in half and scooping out the seeds. Rub each half with olive oil, salt, and pepper. Place the squash halves cut side down on a baking sheet lined with parchment, and bake for 35-45 minutes until tender.
While the squash is cooking, prepare the lentils if you haven't cooked them yet (combine 0.5 cup dry lentils with 1 cup water in a saucepan, bring to a boil, then cover and simmer for 20-25 minutes). A few minutes before the squash is finished, add the diced tomatoes with their juices, garlic, oregano, basil, and salt to a large skillet. Heat for a few minutes before adding the spinach. Cook and stir until the spinach is wilted.
When the squash is finished, prepare the boats by combining the spaghetti squash in each half with half of the lentils and tomato/spinach mixture. Mix until well combined. Top with freshly shredded aged parmesan cheese as desired. Enjoy!
You can cook the spaghetti squash up to 5 days in advance. Store in an airtight container in the fridge until you want to make the recipe. Reheat in the microwave, or add to the skillet with the filling.
Leftovers from the full recipe will last for 3-4 days in the fridge. Reheat in the microwave.
To make vegan, skip the parmesan cheese.
For an extra kick, add red pepper flakes. You can also add shredded chicken or ground turkey.