Place lentils in a soup pot and cover with 2 inches of water. Bring to a boil. Reduce heat to medium-low and simmer until lentils are soft, 25 to 30 minutes. Season with salt during the last few minutes of cooking.
Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Add onion; saute until transparent, about 5 minutes. Add tomatoes and cilantro; cook until tomatoes change color, about 5 minutes. Pour mixture over cooked lentils. Bring to a boil and cook until flavors blend, 3 to 5 minutes more. Serve with banana slices.