Preheat the outdoor grill for medium-low heat. Tightly wrap potatoes in tin foil. Place potatoes on grill, close lid and cook for 40 minutes. Check if potato is done – a fork should easily slide in the potato. Depending on the size, you may need to cook potato for 20-30 minutes more.
While potatoes are cooking, add 3 cups water to a large pot; bring to a boil. Add lentils; bring water back to a boil. Reduce heat to simmer, cover, and cook for 15-20 minutes, until lentils are tender. Remove from pot and set aside.
In the same pot over medium heat, warm oil. Add chopped onion and carrots; cook for 5-7 minutes, until tender and browned. Add garlic; cook for one more minute.Add the BBQ sauce into the pot; stir until all the veggies are coated. Bring to a boil; cover, and reduce to simmer for 10-12 minutes. Add the lentils to the sauce; stir to combine. Add more water if needed.
Add oil to separate saucepan. When heated, add kale to saucepan. Mix with a spatula, until edges are browned.
Slice the potatoes down the middle. Spoon the lentil filling into each sweet potato. Top with sauteed kale.