Place a large heavy bottom pot over medium heat, pour in the olive oil, and allow to heat up.
Add in the onions, garlic, sweet potatoes, bell pepper, and poblano. Stir to combine, and allow to cook for about 10 minutes, whilst stirring occasionally.
Toss in the chili powder, cumin, paprika, oregano, black pepper, and salt, and stir to coat the veggies properly.
Pour in the vegetable broth, black beans, pinto beans, and diced tomatoes with its juices.
Stir properly, and bring the mixture to a boil, but then reduce the heat to medium-low, and allow to cook gently for about 25 minutes.
Stir in the cornstarch mixed with warm water into the pot, and allow to simmer for 10-15 minutes.
Stir in the fresh cilantro, and taste to see if more salt or pepper is needed.
Viola! Your Sweet Potato Chili is ready, top with some diced avocados, tortilla chips, or any other toppings when serving.