Prepare the sweet potatoes: Start by washing and scrubbing the 4 medium sweet potatoes to remove any dirt. Pat them dry with a towel. Using a fork, pierce each sweet potato several times to allow steam to escape during grilling.
Preheat the grill: Preheat your grill to medium heat while you prepare the filling and sauce.
Grill the sweet potatoes: Brush the sweet potatoes with 2 tablespoons of olive oil and sprinkle with salt and pepper. Place them on the grill and cook for approximately 30-40 minutes, turning occasionally, until they are tender when pierced with a fork and have nice grill marks.
Prepare the filling: While the potatoes are grilling, scoop out the flesh of the 2 ripe avocados into a bowl. Add 1 cup of grated Parmesan cheese, 1 teaspoon of garlic powder, and the juice of 1 lime. Mix until you have a smooth, creamy consistency, and season with salt and pepper to taste.
Make the chili-lime sauce: In a small bowl, combine 1 teaspoon of chili powder with the juice of the remaining lime. Add a pinch of salt and mix well.
Stuff the sweet potatoes: Once the sweet potatoes are grilled and cool enough to handle, cut them in half lengthwise. Gently scoop some of the flesh to create space for the filling. Fill each potato half with the creamy avocado-Parmesan filling, pressing gently to pack it in.
Finish and serve: Drizzle the prepared chili-lime sauce over the stuffed sweet potatoes. Serve immediately while warm to enjoy the burst of flavors.