1. Heat oil in a large skillet over medium. Add onion and cook, stirring occasionally, until soft and golden in places, 8 to 10 minutes. Add garlic; cook 30 seconds more. Add ground beef and season with salt. Increase heat to medium-high and cook, breaking into bite-size pieces and stirring occasionally, until meat is browned in places and just cooked through, 6 to 8 minutes. Stir in cocoa, cinnamon, and allspice; cook 1 minute. Stir in tomato sauce, 1 cup water, vinegar, Worcestershire, and chili powder. Bring to a boil, then reduce heat to low and simmer, stirring occasionally, until thick and darkened slightly, 18 to 20 minutes. Remove from heat; cover to keep warm.

2. Meanwhile, bring 2 inches of water to a boil in a large saucepan. Add franks, reduce heat to low, and simmer until plump and hot, about 5 minutes. Drain franks and place in rolls. Top each with chili, sprinkle with onion, drizzle with mustard, and top with cheese. Serve immediately.