Start by preheating your oven to 350°F. While it heats, prepare the mayo spread by combining mayonnaise, lime zest, lime juice, minced garlic, and fresh cilantro in a small bowl. Stir until smooth and well combined, then refrigerate until ready to use. This allows the flavors to meld while you work on the other components.
Heat olive oil in a large skillet over medium heat. Add the minced garlic and cook for 1-2 minutes until fragrant, being careful not to burn it. Pour in the BBQ sauce, pineapple juice, chili powder, and brown sugar, stirring to combine. Let this simmer for 5-7 minutes, stirring occasionally, until the sauce thickens slightly and the flavors deepen. I like to let it reduce a bit so the sauce clings better to the chicken rather than pooling at the bottom of the sliders.
Stir the shredded or cubed chicken into the thickened sauce from Step 2, coating it evenly. Add the pineapple tidbits and gently fold them in, being careful not to break them apart. Let this warm through for 1-2 minutes, then remove from heat. The chicken is now ready to fill your sliders.
Slice your King's Hawaiian rolls in half and arrange the bottom halves cut-side up in a 9x13 inch baking pan. Divide the Hawaiian chicken mixture evenly among the 12 bottom buns, then layer the thinly sliced red onion on top. Place a slice of Monterey Jack cheese on each slider, then spread the lime-cilantro mayo from Step 1 generously on each top bun. Close each slider by placing the top bun over the filling.
Drizzle the melted butter evenly over all the assembled sliders. In a small bowl, combine the finely minced onion, poppy seeds, grated Parmesan cheese, and smoked paprika. Sprinkle this mixture generously over the buttered tops of the sliders. I find that finely mincing the onion into small pieces ensures it cooks through and adds a nice textural element rather than large chunks.
Cover the baking pan tightly with aluminum foil and place it in the preheated 350°F oven. Bake for 25 minutes until the cheese has melted and the buns are warm and slightly golden on the edges. Remove from the oven, carefully lift off the foil (watch for steam), and let the sliders rest for 2-3 minutes before serving. This brief rest helps everything set together so the sliders hold up when you pick them up.