Heat a large pan over medium heat and add the oil. When hot, add the meat, cayenne, cumin and some salt and pepper. Cook, without stirring, until the meat is browned on the bottom, about 5 minutes. Break it up with a wooden spoon, then add the onions and garlic and cook for 2 more minutes.
Add the tomato, liquid, mustard and sugar, if using, to the pan and bring to a simmer; simmer for 5 minutes.
Toast the tortillas or buns. Serve the sloppy joe mixture on the tortillas or buns and top with your favorite toppers.
For more ingredient substitution ideas, see the article below.