Preparation Place beans in medium bowl. Mash with fork until almost smooth. Add sour cream, lemon juice, garlic, and cumin; blend well. Mix in onion and cilantro. Season dip with salt and pepper. Transfer to small bowl. Let stand at least 30 minutes to blend flavors. (Can be prepared 1 day ahead. Cover and refrigerate. Bring to room temperature before serving.) Place dip in center of platter. Surround with vegetables and pita triangles.