In a large bowl toss the sweet potatoes in half of the olive oil. Toss the red peppers with the rest of the olive oil in a separate bowl. Sprinkle both with salt and pepper.
Place the sweet potatoes on the grill. Cook until tender, about 8-10 minutes on each side. With a few minutes remaining in the grilling, add the peppers. Cook them for 2 minutes on each side until slightly charred.
When cool enough to touch, cut the sweet potatoes and red peppers into bite-sized pieces.
Stir in the black beans, green onions, cilantro and lime juice. Salt and pepper to taste.