Brown ground beef in a skillet; drain excess grease if needed.
In a small bowl, whisk flour and water until smooth; add to ground beef with condensed French onion soup. Heat until thick, season with salt and pepper. Set aside.
Preheat oven to 350 degrees F. Spray a 13 x 9 inch baking dish with non-stick cooking spray OR line with foil.
Take the package of Hawaiian rolls, and cut the entire sheet in half creating a rectangular bottom bun and top bun (do not separate into individual slider buns yet).
Layer bottom sheet of buns in the prepared baking dish. Top with prepared French Onion Sloppy Joes, spreading the ground beef mixture from edge to edge.
Sprinkle shredded cheese over the French Onion Joes; add the top rectangular bun.
In a microwavable bowl, melt butter. Add dried minced onion, Worcestershire sauce, salt and mustard and stir until combined. Pour over the top of the sliders, spreading it to cover all buns and allowing it to drip over the sides.
Let the buns sit for 10 minutes to absorb the butter mixture.
Cover tightly with foil; bake for 15 to 20 minutes or until the cheese is melted.
Cut into individual sliders.