Preheat your oven to 375°F (190°C).
Heat olive oil and 1 tbsp butter in a skillet over medium heat. Add diced onions and cook until caramelized and softened. Add a splash of water to help the onions soften faster if needed.
Once onions are caramelized, add the ground beef to the skillet. Cook until browned and no longer pink. Drain any excess fat. Season with mustard, chicken bouillon, Sazon, garlic powder, onion powder, salt, and pepper.
Add 2 slices of American cheese to the beef mixture and toss until the cheese melts and coats the meat.
In a bowl, melt 3 tbsp of butter. Stir in garlic paste and parsley. Set aside.
In a small bowl, combine mayo, mustard, ketchup, dill relish, smoked paprika, garlic powder, and onion powder. Mix well and set aside.
Heat the griddle or skillet. Cut slider buns in half and toast them face down until golden brown in a bit of melted butter.
Spread a layer of special sauce on the bottom half of each slider bun. Add a scoop of the cheesy meat mixture and top with another slice of American cheese if desired. Add more sauce to the top bun and place it over the meat.
Brush the tops of the slider buns with garlic butter. Bake in the preheated oven for 20-25 minutes, or until the cheese is fully melted and the buns are golden.
Cut into individual sliders and serve immediately. Enjoy these melty, cheesy bites!