Preheat the oven to 350℉. Line a rimmed baking sheet with parchment paper.

Lay the breads on the baking sheet and toast for 3 minutes. Turn the breads over and toast for another 2-3 minutes. Remove from the oven.

While the breads are toasting stir together the onion, mayonnaise and parmesan cheese in a medium sized bowl. Spread the mixture on the breads. Sprinkle the tops with dashes of paprika.

Broil the toasts for 2-4 minutes, depending on the oven, until the onion mixture is lightly browned and bubbly. Serve immediately.