Heat a large heavy pot over medium heat. When hot, add the cumin and chili powder, spreading it out into a thin layer. Stir as the spices become toasted and develop a wonderful aroma, for 2-3 minutes. Transfer the toasted spices to a bowl and set aside.
Add the olive oil, chili peppers, and garlic into the skillet and saute until the garlic is tender, 2-3 minutes.
Add the canned tomatoes including all the juices, the lentils, and 2 cups of water. Turn the heat up to high, bring to a boil, then reduce to medium-low and simmer for 5 minutes.
Add the sweet potatoes, 2 more cups of water, and the toasted spices. Once the pot has returned to a boil again, reduce the heat to low, cover the pot, and simmer for at least 25 minutes, stirring occasionally. The chili is finished cooking when both the lentils and the sweet potatoes are tender to your liking.
Add 2 Tablespoons of soy sauce, stir well, and taste the chili. If you’d like it saltier, add another tablespoon.
Garnish with avocado and hot sauce as desired and serve.