Melt the oil in a large, deep skillet over medium heat (or heat the coconut milk).
Add the onion, garlic, and crushed red pepper.
Cook over medium heat for 3 minutes, then stir in the collards and sweet potato.
Add the beans, tomatoes with their juice, water, and coconut milk.
Bring just to a boil, lower the heat to medium-low, and cook, covered, until the collards and sweet potato are tender, about 30 minutes.
Season with salt and pepper and serve.