Preheat oven to 400°F. and line a baking sheet with foil. Place the diced sweet potatoes on the sheet pan. Drizzle with olive oil and season with the first amounts of chili powder, salt and pepper. Toss until coated and place in the oven to roast for approximately 20 minutes or until they're tender.
While the sweet potatoes roast, heat a medium sized saucepan over medium heat. When hot, add in the olive oil and diced onion. Saute 2 to 3 minutes and then add in the garlic and spices. Saute another minute then stir in the tomato paste and add in the lentils. Pour the vegetable broth in and stir everything together. Bring to a boil then reduce the heat to medium-low, cover the saucepan partially with a lid and simmer for 20 to 30 minutes or until the lentils are tender.
In a blender or food processor add all of the ingredients for the avocado crema and blend until smooth. Add water a tablespoon at a time to loosen in until desired consistency is reached.
Fill warmed corn tortillas with the lentils, sweet potatoes and topped with the avocado crema, red onions and cilantro.
This nutritional information refers to each serving of the entire recipe and not just the products used as ingredients.