Coat a 5-quart or larger slow cooker with nonstick spray. Rinse the lentils, then add them to the slow cooker. Add the sweet potato, vegetable broth, water, shallot, curry paste, garam masala, turmeric, sugar, ginger, salt, garlic, and tomato paste. Stir well to combine. Cover and cook on HIGH for 3 to 4 hours or LOW for 6 to 7 hours, until the lentils and sweet potatoes are tender. Turn off the heat and stir in the coconut milk. If you’d like a thinner consistency, stir in additional broth or water.
Taste and adjust seasoning as desired. Serve hot over prepared brown rice or quinoa. Garnish with lots of fresh cilantro and a squeeze of lemon or lime.