Preheat a sauté pan over medium heat and add the olive oil. Season the chicken breast with kosher salt and freshly ground black pepper. Cook the chicken for 3 to 4 minutes on the first side, then reduce the heat slightly and continue cooking on the second side until the internal temperature reaches 165°F (74°C). Remove the chicken from the pan, allow it to rest briefly, then shred.

In the same sauté pan, add the diced onion and minced garlic. Cook over medium-low heat for 4 to 6 minutes, stirring occasionally, until the onion is softened and fragrant. Remove the pan from the heat.

In a large mixing bowl, combine the shredded chicken, cooked onion and garlic, diced tomato, chopped pickled jalapeños, jalapeño brine, mayonnaise, shredded Monterey Jack cheese, and sliced green onions. Mix until evenly combined. Taste and adjust seasoning as needed.

Preheat the oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish. Arrange the bottom halves of the slider buns evenly in the prepared dish.

Place the cheddar cheese slices over the buns, then spread the chicken mixture evenly on top. Arrange the reserved jalapeño slices over the filling and sprinkle evenly with the fried onions.

Place the top halves of the slider buns over the filling. Brush the tops evenly with melted butter and lightly season with freshly ground black pepper.

Bake uncovered for 18 to 20 minutes, or until the cheese is fully melted and the sliders are heated through. Remove from the oven and allow to rest briefly before slicing and serving.