Heat the oil in a large skillet over medium heat. Add the onion, bell pepper, and garlic. Cook until they are tender, about 5 minutes.
Increase the heat to medium-high and add the ground beef. Cook, breaking up the beef with the edge of a spoon, until no longer pink, about 5 more minutes. Drain off any excess fat.
Reduce heat to medium-low. Add the salt, pepper, chili powder, tomato paste, mustard, and coconut aminos. Stir until well combined. Remove from heat and cover until ready to assemble.