Buttery Co Jack Swiss Pastrami Sliders

Name: Buttery Co-Jack & Swiss Pastrami Sliders
Ingredients: 1 Family-Sized pkg. Hawaiian Rolls (18 ct.); 18 pieces of torn kale leaves; 18 thin slices deli pastrami; 9 slices co-jack cheese, quartered; 9 slices swiss cheese, quartered; 1/3 cup mayo; 1 1/2 tsp. hot horseradish sauce; For Onions:; 1 large red onion, sliced or chopped; 3 Tbl. butter; 1/2 tsp. minced garlic; 1/4 tsp. each salt and coarse ground black pepper; For Butter Sauce:; 1 stick butter, melted; 1 tsp. worcestershire sauce; 1 tsp. spicy brown mustard; 1 tsp. onion powder; 1 Tbl. poppy seeds