Melt butter & oil in a large skillet with high edges over medium heat. Add diced onion with a pinch of salt and saute for 5 minutes.
Add minced garlic and cook until fragrant. Then add 1 tablespoon balsamic vinegar and saute for 5 more minutes.
Add pre-cooked lentils, half a jar of marinara sauce, 1 tablespoon balsamic vinegar, and salt and pepper to taste. Cook until heated through and your pasta is done. The longer you cook, the more the flavors will have time to come together.
Meanwhile, bring a pot of heavily salted water to a boil and cook 8oz of spaghetti according to the package instructions. Drain when done and set aside.
To serve, place the spaghetti in bowls and top with as much sauce as desired! You could also combine the pasta with the sauce and mix together in the pan.
Top with basil, vegan parm, balsamic glaze, and/or red pepper flakes and enjoy!