Prep. Preheat the oven to 350°F. Then, line a 9x13-inch pan or 10x15-inch baking sheet with parchment paper.
Marinate the chicken. In a medium-sized bowl, combine the diced chicken, 2 tablespoons olive oil, ½ teaspoon garlic salt, ½ teaspoon oregano, and ¼ teaspoon pepper. Let the chicken marinate at room temperature as you get the other ingredients ready.
Prepare the cream cheese mixture. In a medium bowl, mix the softened cream cheese using a stand mixer with a paddle attachment or an electric mixer. Then, add the sour cream and mix it well. After that, set it aside.
Cook the chicken. Heat a 10 or 12-inch skillet over medium-high heat. Then, add the marinated chicken and cook for 5-7 minutes, stirring occasionally, until the chicken is fully cooked. Transfer the chicken to a large plate and set aside.
Cook the spinach. In the same skillet, add 1 tablespoon olive oil. Add the chopped spinach and artichokes, and cook over medium heat until the spinach is wilted, about 3-5 minutes, stirring occasionally.
Combine filling. Put the cooked chicken back in the skillet with the spinach and artichokes. Then, off the heat, mix in the cream cheese mixture, ¾ cup shredded mozzarella cheese, ½ cup grated Parmesan cheese, 1 ¼ teaspoon garlic salt, and ½ teaspoon coarsely ground pepper. Keep mixing until it's all combined evenly.
Assemble sliders. Using a long serrated knife, cut the rolls in half horizontally, keeping the rolls together in one big piece. Place the bottom halves of the rolls on the prepared baking sheet. Spread the chicken and spinach mixture evenly over the bottom halves. Sprinkle the remaining ¾ cup shredded mozzarella cheese over the filling. Place the top halves of the rolls back in position.
Prepare the topping. In a small bowl, whisk together the melted butter, ½ teaspoon oregano, ½ teaspoon garlic powder, ¼ teaspoon garlic salt, 2 tablespoons grated Parmesan cheese, and 2 tablespoons freshly minced parsley. Brush this mixture over the tops of the rolls.
Bake. Cover the sliders with aluminum foil and bake in the preheated oven for 20 minutes. Remove the foil and bake for an additional 3-5 minutes or until the tops are golden brown. Carefully remove from the oven and, if desired, brush with additional garlic butter.
Serve. Let the sliders cool for a couple of minutes before cutting and serving. Enjoy them warm and fresh.