1 cup red lentils
3 cups water
1 medium yellow onion, finely chopped
1 hot pepper, finely chopped
1 cup tomato sauce
1 can cooked kidney or red beans
1 teaspoon cumin seeds
1/2 teaspoon salt
1 tablespoon vegetable oil
1 lime

1. In a large pot, bring the lentils and water to a boil. Add the hot pepper and salt, and continue boiling over medium-low heat until the lentils are tender, around 20 minutes.
2. Add the tomato sauce and beans, and continue cooking for 5 minutes.
3. In the meantime, cook the onions, cumin seeds, and oil in a frying pan until the onions start to brown.
4. Squeeze the juice from the lime onto the soup and mix. Pour the onions and cumin seeds over the soup and serve.