Spray a large skillet with nonstick cooking spray.
Turn the heat to medium-high and add the diced onion to the skillet. Sauté for two minutes.
Add the chopped pepper to the skillet and sauté for two minutes.
Add the ground beef to the skillet and mix with the vegetables. Cook until no pink remains.
Add the minced garlic and cook for about 30 seconds.
Then, add in the tomato paste and stir until it's well combined.
Add the remaining ingredients to the skillet: water, mustard, tomato sauce, salt, Worcestershire sauce, chili powder, paprika, and crushed red pepper flakes. Stir until well combined.
Reduce the heat to low and simmer for about ten minutes. The mixture should be thick.
Scoop into toasted hamburger buns and store in an airtight container .