Step 1

Preheat oven to 450°F. Poke each sweet potato a few times with the prongs of a fork. Wrap each potato in foil. Place on center oven rack and bake for 60 to 80 minutes, until fork tender.

Step 2

While potatoes bake, heat oil in a large skillet with a fitted lid over medium heat. Add shallot; cook 2 to 3 minutes, until softened. Add garlic; cook 1 minute, until aromatic. Add tomato paste and red pepper flakes; cook 1 minute, stirring often. Stir in smoked paprika, salt, black pepper, and lentils; cook 1 minute, stirring to coat lentils. Add broth and water, bring mixture to a simmer over medium-high. Reduce heat to medium-low, cover, and cook 20 to 22 minutes, stirring occasionally, until lentils are tender and have absorbed most of the liquid. Stir in chopped walnuts.

Step 3

Slice sweet potatoes down the center, lengthwise. Fill evenly with lentil mixture. Garnish with fresh cilantro, yogurt, and avocado, if desired.