Heat the olive oil in a large sauté pan over medium heat. Season the chicken breast generously with salt and black pepper. Add the chicken to the pan and cook for 3–4 minutes on the first side, until lightly golden. Reduce the heat, flip the chicken, and continue cooking until the internal temperature reaches 165°F. Remove from the pan and allow the chicken to rest briefly before shredding.

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

Add the diced tomato, chopped jalapeños, jalapeño brine, mayonnaise, shredded chicken, and Monterey Jack cheese to the pan. Stir until fully combined. Taste and adjust seasoning with additional salt and pepper as needed.

Preheat the oven to 350°F. Arrange the bottom halves of the slider buns in a 9×13-inch baking dish. Place the cheddar cheese slices evenly over the buns, followed by the chicken mixture. Top with the reserved jalapeño slices and fried onions.

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

Bake for 18–20 minutes, or until the cheese is fully melted and the sliders are heated through. Remove from the oven, allow to rest briefly, then slice and serve.