Heat the oil in a large pot over medium heat. Add the onion and fry until beginning to soften - about 3 minutes. Add the garlic and bell peppers and continue frying until the bell peppers are soft - about 4 - 5 minutes.

Add the tomato paste, chili powder, cumin, oregano and paprika and fry, stirring continuously, for about 2 minutes or until the tomato paste darkens slightly.

Add the sweet potato, black beans, cocoa powder, vegetable stock and tomatoes with their juices. If using whole canned tomatoes, break them up with your hands as you add them.

Raise the heat to bring the chili to a boil then reduce the heat to medium-low to keep it simmering.

Simmer until the sweet potatoes are tender - about 20 - 30 minutes, depending on how big you diced them. If the liquid seems to be reducing too much, add another splash of vegetable stock or water.

Add the soy sauce and taste your chili. You can add a pinch of salt to bring together the flavors more if you think it’s necessary.