Peel and grate the ginger using a small holed cheese grater. Mince the garlic, and dice the onion. Sauté the onion, ginger, and garlic in a large pot with the olive oil over medium heat for 2-3 minutes, or until the onion becomes soft and translucent.
While the onion, ginger, and garlic are sautéing, peel and dice the sweet potato into 1/2-inch cubes. Add the sweet potato cubes, cumin, and red pepper to the pot and continue to sauté for about 5 minutes.
Add the tomato paste, peanut butter, and vegetable broth to the pot. Stir until the peanut butter and tomato paste have mostly dissolved into the broth. Place a lid on the pot and turn the heat up to high. Allow the stew to come up to a boil. Once it reaches a boil, turn the heat down to medium-low and allow it to simmer for 15-20 minutes, or until the sweet potatoes are very soft.
While the soup is simmering, prepare the collard greens. Use a sharp knife to remove each stem (cut along the side of each stem), then stack the leaves and cut them into 1/2-inch wide strips. Place the chopped collard greens in a colander and rinse very well
Once the stew has simmered for 15-20 minutes and the sweet potatoes are very soft, stir in the collard greens. Let the stew simmer for about 5 minutes more, then begin to smash the sweet potatoes against the side of the pot to help thicken the stew.
Finally, taste the stew and add salt or red pepper, if desired. Serve the stew with a scoop of cooked rice (about 3/4 cup), a few chopped peanuts, fresh cilantro, and a drizzle of sriracha, if desired.