Add the rinsed red lentils, chopped onion, minced garlic, grated ginger, diced tomatoes, and vegetable broth to the slow cooker.
Stir in the ground cumin, ground turmeric, garam masala, chili powder, and salt until evenly combined.
Cover and cook on low for 6 hours or on high for 3 hours, until the lentils are soft and the stew has thickened.
Stir in the coconut milk and let the stew sit for 5 minutes to warm through.
Serve over cooked rice and top with fresh cilantro.