Boil red lentils in 3 cups of water for 15 minutes until soft, then drain and press out excess moisture.
Steam or boil sweet potato cubes until fork-tender, then mash in a large bowl until smooth.
Combine the mashed sweet potatoes, cooked lentils, breadcrumbs, onion, garlic, cumin, paprika, egg, salt, and pepper in the bowl.
Shape the mixture into 8 uniform patties, approximately 3/4-inch thick.
Heat olive oil in a large skillet over medium heat.
Fry the patties for 4 to 5 minutes per side until a golden-brown crust forms.
Prepare the sauce by processing avocado, Greek yogurt, cilantro, and lime juice in a blender until smooth.
Serve the warm patties immediately with a dollop of the avocado cilantro sauce.