In a large pot over medium heat, toast the spices for 30 seconds while stirring constantly. Add the onion and 1/3 cup of the water then cook for 5 minutes, until translucent.Whisk in the coconut milk and the remaining 2/3 cup water, and bring to a boil.Add the sweet potatoes, decrease the heat to medium-low, cover and rapidly simmer for 15 minutes, until potatoes are fork tender. Stir occasionally while cooking.Spoon the curry into bowls with warm basmati rice. Top with a squeeze of lime juice, scallions and cilantro. Serve warm with whole grain naan and enjoy!