01 -
In a large skillet over medium-high heat, combine the diced onion and ground beef. Season with beef bouillon powder, salt, and pepper. Cook until the beef is no longer pink.
02 -
Add minced garlic to the skillet and cook for an additional 30 seconds, then drain excess grease.
03 -
Stir in tomato sauce, ketchup, mustard, and brown sugar. Bring to a simmer over low-medium heat, blending flavors.
04 -
Heat a separate skillet over medium heat. Spread a thin layer of mayonnaise on one side of each bread slice and place mayonnaise side down in the skillet. Layer one slice of cheese, a portion of the sloppy joe mixture, and another slice of cheese on the bread. Top with a second piece of bread, mayonnaise side up.
05 -
Cook each sandwich until both sides are golden brown and the cheese has melted, flipping carefully.
06 -
Serve immediately while hot.