Add the lentils and 2 cups of water to a pot. Bring to a boil, and simmer for 8 minutes. Add in the cubed butternut squash and simmer until both the squash and lentils are tender, about 7-12 more minutes. Drain any excess water and set aside.
In a large skillet, heat the avocado oil over medium-high heat. Add in the onion, and cook until translucent, about 7-10 minutes. Add in the garlic, tomato paste, mustard powder, cumin, and paprika. Sautee for another 30 seconds. Add in the tomato sauce, pumpkin puree, and maple syrup. Cover and simmer for 10 minutes.
Add in the apple cider vinegar, and stir to combine. Remove from the heat and serve with buns, over potatoes, or as desired.