Heat the broiler to 500 degrees.
Combine the oil, onion and bell pepper into a sauce pan and cook over medium heat. Add the crushed tomatoes, butter, sugar, onion powder, garlic powder and kosher salt. Cook for 15 minutes. Add the vinegar and cook for an additional two to three minutes.
Place chicken into a bowl and add enough sauce to cover the chicken, but not soak it. On one side of the bun, add chicken mixture and top with slices of cheese. On the other bun, add caramelized onions. Continue this process until the buns and chicken have been used.
Place the two sides of the buns on a baking sheet and place in the oven. Broil until the cheese is melted and the buns browned. Remove from the oven and place the two sides together and serve warm.