Preheat the oven to 350°F and line a baking sheet with parchment paper.

In a large skillet over medium-high heat, cook the ground beef with diced onions and minced garlic until browned and no longer pink, breaking apart as it cooks. Drain excess grease.

Transfer the cooked beef to a large bowl and mix in secret sauce, salt, black pepper, smoked paprika, and garlic powder.

In the same skillet, cook bacon until crispy, then crumble into bite-sized pieces.

Slice the slider buns horizontally without separating the tops from the bottoms and place the bottom halves on the prepared baking sheet.

Layer 6 slices of cheddar cheese evenly over the bottom buns.

Spread the seasoned beef mixture evenly over the cheese.

Add the remaining 6 slices of cheddar cheese on top of the beef, then sprinkle with crumbled bacon.

Place the top halves of the buns over the fillings.

In a small bowl, combine melted butter, Dijon mustard, brown sugar, and Worcestershire sauce. Warm slightly if needed and stir to mix.

Brush the butter mixture evenly over the tops of the buns and sprinkle with sesame seeds.

Tent the sliders with foil and bake for 15–20 minutes.

Remove the foil and bake for an additional 5 minutes if a toasted top is desired.

Serve warm, optionally adding pickles, red onion, tomato slices, or shredded lettuce.