Place sweet potatoes and onions and 2 tablespoons olive oil on a baking sheet; toss well. Bake, turning occasionally, until edges brown, 30 to 40 minutes.
Place jalapenos, garlic, lime juice and 2 tablespoons olive oil in a blender or food processor and process until blended.
Toss warm sweet potatoes and onions, beans, and bell pepper in a large bowl. Add dressing, salt and pepper. Toss well. Top with cilantro. Serve room temperature.