Add red lentils, diced tomatoes, coconut milk, broth, onion, garlic, turmeric, cumin, coriander, salt, and chili flakes to the crockpot. Mix well.
Cover and cook on low for 6-7 hours or high for 3-4 hours, until the lentils are soft and the dahl is thick and creamy.
Stir in lime juice before serving. Garnish with extra coconut milk, cilantro, and more chili flakes if desired. Serve with cooked basmati rice and naan.