Line a large baking sheet with parchment paper. Lay the slices of cocktail bread evenly out over it, in a single layer.
1 loaf cocktail rye or cocktail pumpernickel rye bread
Add all of the remaining ingredients, except paprika, to a medium sized mixing bowl. Stir to evenly combine.
1 1/2 cups mayonnaise, 2/3 cup grated Parmesan cheese, 3 tbsp finely minced white onion, 1/8 tsp Worcestershire sauce, 1/2 tsp seasoning salt, 1/2 tsp garlic powder, 1/2 tsp cracked black pepper
Spread the topping evenly out over the sliced bread. Sprinkle with smoked paprika, if using.
smoked paprika, for garnish
Place the pan in the oven, under a hot, broiler and watch the slices carefully. Cook until the cheese is golden brown on top, and the mixture's 'puffed' a bit. Do not leave them unattended as they will go from perfect to burnt quickly.
Remove the cocktail bites from the oven, and serve warm.