In a medium pot, combine the sweet potatoes and vegetable broth or water. Bring to a boil, then reduce heat and simmer until the sweet potatoes are tender, about 15 minutes. Drain and set aside.
In the same pot, add the red lentils and 2 cups of water. Bring to a boil, then reduce heat and simmer until the lentils are soft, about 15 minutes. Drain any excess water and set aside.
In a large bowl, mash the cooked sweet potatoes and lentils together until smooth. Stir in the chopped onion, minced garlic, cumin, smoked paprika, salt, pepper, breadcrumbs, and parsley until well combined.
Form the mixture into patties, about 2-3 inches in diameter. Place them on a plate or baking sheet.
Heat olive oil in a large skillet over medium heat. Once hot, add the patties in batches, cooking for about 4-5 minutes on each side until golden brown and crispy. Remove and drain on paper towels.
For the avocado sauce, combine the avocado, lime juice, Greek yogurt, garlic powder, salt, and pepper in a blender or food processor. Blend until smooth and creamy.
Serve the crispy patties warm with a drizzle of avocado sauce on top.