Place the lentils, onion and 8 cups water in a large pot and bring to a boil. Reduce heat to simmer and skim off any scum or foam with a slotted spoon. Add the rice, partially cover, and cook until the rice is done, about 30 minutes. Add the garlic and the tomato paste, mixing well. Add lemon juice, salt and pepper to taste, and place soup in large serving bowl.

In a small skillet melt the butter until it sizzles, remove from the heat, and stir in the mint and Aleppo pepper, if desired, mixing well. Pour over the soup and serve.