Heat oil in a Dutch oven or a large saucepan over medium heat.
Dice onion and add to the saucepan; cook about 5 minutes until softened, stirring frequently.
Meanwhile, chop sweet potatoes into bite-size pieces, and drain and rinse the black beans. Set aside separately.
Add the chili powder and cumin to the onion, then add the broth and sweet potatoes; stir well to combine.
Bring the mixture to a gentle boil, then cover, reduce heat to low, and simmer for 15 minutes until the potatoes are almost tender.
Add undrained tomatoes and black beans; continue to simmer, uncovered, about 15 minutes more until the mixture is heated through and slightly thickened.
Zest the orange; stir 2 teaspoons zest into the chili, and season with salt and pepper to taste.
While chili is cooking, preheat oven to Broil.
Spread butter evenly onto each slice of bread, then sprinkle with garlic powder and place onto a baking sheet.
Place bread under the broiler for 1-2 minutes until golden brown. Watch closely so it does not burn!
Serve chili topped with green onions and sour cream as desired; serve toast and apple slices on the side.