In a medium saucepan, combine lentils, broth, water, and turmeric. Bring to a boil, reduce heat, and simmer, stirring occasionally, until the lentils are tender, about 20 minutes.
Meanwhile, melt butter in a small saucepan; add garlic, cumin seeds, and crushed red pepper. Cook, stirring, until fragrant, about 3 minutes.
Remove the lentils from heat, and stir in the garlic mixture, diced tomato, mint, and salt. Serve warm.