WASH the bell peppers and celery. Dice the onions, peppers, and celery. (See note #1.) Measure out the sauce ingredients.
BROWN the meat in a skillet. Sprinkle in the Montreal steak seasoning. If you have several pounds of meat, do it in batches. Set it aside. (See note #2.)
SAUTE the onions, peppers, and celery in the olive oil in a large soup pot on the stove. Cook until they are softened (about 5 to 7 minutes).
STIR in the tomato sauce, brown sugar, vinegar, Worcestershire sauce, mustard, onion powder, paprika, garlic powder, and allspice into the soup pot.
COVER the pot and cook over medium-low heat until it starts to bubble. Cook for 10 minutes or until the veggies are soft and the sauce is as thick as you like.
ADD the ground beef to the sauce. Stir and cook over medium-low heat for 10 to 15 minutes.
OPTIONAL: If you want to thicken the sauce, mix the cornstarch into a bowl with cold water. Stir until it is smooth. Then slowly stir the cornstarch mixture into the sloppy joes meat. Bring to a boil and boil one minute.
SERVE immediately, or transfer the filling to a slow cooker to keep it warm for the party.
OPEN a bun and scoop ½ cup of filling on it. Top with cheese, coleslaw, or Fritos.