Heat olive oil in a large heavy-bottomed pot over medium heat until shimmering. Add the diced onion and cook for 3-4 minutes, stirring occasionally, until translucent and fragrant.
Add the minced garlic, chili powder, and smoked paprika to the onions, stirring constantly for about 1 minute until the spices are fragrant and slightly darkened.
Add the diced sweet potatoes to the pot, stirring to coat them evenly with the spices. Cook for 2 minutes, letting the potatoes start to develop a bit of color.
Pour in the vegetable broth and the can of diced tomatoes with juices. Bring the mixture to a gentle simmer, then reduce the heat to low and cover the pot.
Let the chili simmer on low heat for about 4 to 6 hours, stirring occasionally. As it cooks, the sweet potatoes will soften completely and the flavors will meld together, creating a thick, rustic stew.
About 15 minutes before serving, stir in the rinsed and drained black beans. Season with salt and pepper to taste, and simmer uncovered for the final few minutes to heat through.
Remove from heat, give it a final stir, and let sit for a few minutes. Serve the chili hot, garnished with your favorite toppings like fresh cilantro, avocado slices, or shredded cheese.