Heat the olive oil in a large Dutch oven or heavy-bottomed pot over medium heat. Add the diced onion and red bell pepper, sautéing until softened and translucent, about 5 to 7 minutes.

Stir in the minced garlic, chopped chipotle peppers, smoked paprika, and ground cumin. Cook for 1 minute until highly fragrant, stirring constantly to prevent the spices from burning to the bottom of the pot.

Add the cubed butternut squash, dry brown lentils, fire-roasted diced tomatoes with their juices, and vegetable broth. Stir well to combine all the ingredients and bring the mixture to a rolling boil.

Once boiling, reduce the heat to low, cover the pot, and let it simmer gently for 35 to 40 minutes. Stir occasionally to prevent the lentils from sticking, cooking until both the lentils and squash are tender.

Remove the lid and allow the chili to simmer uncovered for an additional 5 minutes so the broth can thicken slightly. Taste the chili and stir in the kosher salt, adjusting the seasoning as needed.

Ladle the thick, smoky chili into warm bowls. Garnish with fresh cilantro, diced avocado, or a dollop of dairy-free sour cream before serving.