T's Sweet Potato Chili

I enjoyed this a lot. It was better the second day with tortilla chips. Next time I make it I'm going to cube the sweet potato into smaller cubes (mine were kind of large) to balance out the lime thoroughly.

1 pound hamburger, browned (optional)
2 tablespoons extra-virgin olive oil
1 medium red onion, chopped
1 tablespoon minced garlic
2 teaspoons salt
1 large sweet potato, cut into 1/2-inch cubes [or maybe two small potatoes for easier chopping]
Juice of 1 lime
1 28-can diced tomatoes
1 15-ounce can black beans, rinsed and drained
1 15-ounce can chili beans (I usually use bush's red chili beans in hot sauce)
1 tablespoon cumin
1 tablespoon chili powder
1 teaspoon cocoa powder

Warm the oil in a large pan over medium heat and add the onion, garlic, and salt. Saute until soft, about 4 minutes.

Add the sweet potatoes, and cook 15 minutes more, continuing to stir occasionally.

Add the hamburger, tomatoes, beans, lime juice, cumin, chili powder, and cocoa, bring to a simmer, cover, and cook until potatoes reach desired tenderness (I like my potatoes soft - when I have time, put it on the lowest heat setting and let it go for about 3 hours. When you don't have that much time, turn it to medium and it usually only takes about 20-30 minutes).