Preheat oven to 350°F. Line an 11×15 inch baking dish with foil and lightly spray with nonstick spray.

Slice the slider rolls in half; set the tops aside and place the bottoms in the prepared dish.

In a small bowl, whisk together mayonnaise, ketchup, and mustard. Set aside.

Heat olive oil in a large skillet over medium heat. Add diced onions and cook until soft and golden.

Add ground beef to skillet; cook until no pink remains, breaking it apart as it cooks.

Drain excess fat, then stir in French Onion Soup Mix and Steak Seasoning.

Remove from heat. Mix in mayonnaise mixture and coat beef evenly.

Spread beef mixture over the bottom roll layers. Top with cheese slices, then with pickle slices. Cover with the top roll layer.

Brush melted butter over the top and sprinkle with sesame seeds.

Cover with foil and bake for 15-20 minutes until cheese melts. Let stand for 5-10 minutes before serving.