Preheat the oven to 375°F. Grease and line a 9x9 baking dish with parchment paper. Use the parchment overhang to create “wings” on either side of the pan. Press the ground beef into the shape of the pan and season generously with salt and pepper. Bake the patty for about 15-25 minutes.
Slightly tilt the pan to drain the excess fat from the pan. Let the burger patty cool in the pan for 5-10 minutes before lifting it out of the pan with the overhanging parchment. Place on a separate plate to cool. Clean the pan while the burger patty cools.
Decrease the oven temp to 350°F. Grease the baking sheet lightly with cooking spray then arrange the bottom half of 9 sliders (or however many will fit in your pan, there should be enough to fill the pan edge to edge).
Place the burger patty on top of the slider bottoms and remove the parchment. Spread on the mayonnaise and top with the American cheese, tomato, jalapenos, and fried onions as desired. Top with more cheese to glue everything together then place on the top bun.
In a small bowl, melt the butter and whisk it together with the honey mustard, everything seasoning, and parsley. Brush the mixture on top of the buns then return to the oven and bake for an additional 10-15 minutes, until golden brown and the cheese is melted.
Sprinkle on the remaining parsley and use a sharp knife to cut the sliders into individual burgers. Serve hot and enjoy!