Toss the beef with 1 tablespoon each of brown sugar and salt in a large bowl. Heat the vegetable oil in a large skillet over medium-high heat. Cook the beef in batches until browned on all sides, 4 to 5 minutes. Transfer to a 5 to 6 quart slow cooker.
Reduce heat to medium, add the onions to the skillet and cook until soft, about 5 minutes. Stir in the garlic, chilies, cumin, and chili powder and cook 3 minutes. Add 1 1/2 cups water and the tomatoes and simmer, scraping up the browned bits from the bottom, about 3 minutes. Transfer to the slow cooker, cover and cook on low for 7 hours.
Add the remaining 1 tablespoon of brown sugar and the hot sauce (optional) to the chili. Serve with green onions, cilantro, and sour cream for topping.