Brown the ground beef in a large skillet over medium high heat. Use a spatula to chop the beef into small bits.
Drain the grease from the beef and place the beef in a small bowl, allowing about a tablespoon of grease to remain in the skillet.
Use a food processor or a chef’s knife to mince the bell pepper into small pieces.
Put the bell pepper into the skillet and saute it in the grease until it is soft and cooked through. This should take about 3 to 5 minutes.
Add the garlic to the peppers and saute all of this together for about a minute until the garlic is light brown and fragrant.
Add the beef to the skillet and stir to combine. Turn the heat down to low.
Measure the ketchup into a measuring cup and add the brown sugar, water, mustard, chili powder, Worcestershire sauce, salt, pepper, and the red pepper flakes. Stir these together with a spoon until combined.
Then add them to the skillet along with the beef and peppers.
Add the tomato paste and use a spatula to combine all the ingredients. You may have to turn and mash the mixture to ensure that the tomato paste is thoroughly incorporated.
Cook the mixture over low heat until it is heated through. If it is too runny, let it simmer uncovered for about 5 minutes or until it is thick enough to scoop onto a hamburger bun.
Serve about ½ to ¾ cup of this mixture on hamburger buns. Buns that are lightly toasted add to the texture of these special sandwiches.
Allow leftovers to cool completely before storing in an airtight container for up to 5 days. Reheat in the microwave for about 30 seconds. Stir and heat it again for another thirty seconds if needed.