In a large skillet add oil and heat over medium-high heat. Once the oil is simmering, reduce heat to medium and add onions and salt and sauté, stirring often, until onions are translucent and beginning to brown around the edges, about 6-10 minutes.

Stir in garlic powder and chili powder and cook until fragrant, bout 20 seconds.

Add in beef and use the back of a wooden spoon to break the meat apart. Cook until the meat is almost browned all the way through.

Stir in brown sugar, tomato puree, ketchup, water, and Worcestershire sauce. Simmer the mixture until the sauce has thickened, about 5-10 minutes. Season mixture with pepper.

Cut 12 slices of bread from the French bread loaf that are each about 1-inch thick.

Brush the top side of each slice of bread with melted butter. Turn over 6 slices of bread and evenly distribute the sloppy joe filling among them.

Top the sloppy joe filling with 1/3 cup of cheddar cheese. Cover with the remaining bread slices, with the buttered side up.

Over medium-low heat, heat a large nonstick skillet for 1 minute.

Carefully place 2 sandwiches in the pan. Cook until the first side is golden brown, about 3-5 minutes.

Flip the sandwiches over, press lightly with your spatula, and cook until golden brown, about 2 minutes. Repeat the process with the remaining sandwiches.

Slice and serve!