Cut breasts in half horizontally, pound evenly to ¼ inch thick. Cut each piece in half vertically to create slider sized pieces. Place into a large zip-top bag or bowl. Add several tablespoons of blackened seasoning and a few tablespoons of olive oil. Mix to coat them evenly, making sure they are well seasoned on all sides. Allow to marinate while prepping other ingredients.
Mix together the butter garlic and parsley in a bowl. Heat together for 20 seconds in the microwave or until partially melted. Set aside.
Cook chicken in an oiled skillet over medium-high for about 3 minutes or until they are perfectly charred on the underside (not burnt). Flip once and reduce heat to low. Add one tablespoon of garlic butter mixture into the pan and allow it to melt with the chicken as it cooks, about 5-6 minutes or until internal temp reaches 165 degrees.
Place sliders cut-side up onto a baking sheet and toast under a broiler until golden brown, just a few minutes. Flip the top buns so the domed tops are facing up and leave them beside the bottom buns on the pan. Spread the tops with garlic butter, sprinkle on parmesan. To the bottom buns, add an even layer of cheese. Broil until cheese softens, about 1-2 minutes.
Add the chicken evenly among the bottom buns and top them with bacon. Flip the top buns and add an even layer of cheese. Return the pan to the broiler to melt the cheese and warm the chicken and bacon, another minute or two.
Drizzle on ranch, then add tomato slices, red onions and lettuce. Another drizzle of ranch over the lettuce. Add top buns on, slice and serve. Use sandwich-sized toothpicks for easier handling.