Please dehydrated onions in water to reconstitute them for 30 minutes. Drain and pat dry.
Heat over to 375F
Lay cocktail breads on a baking sheet. If you wish the bottoms to be crisp, place cooling rack in baking sheet and place bread on cooling rack.
On half the slices of bread add a layer of mayonnaise. This should be thick enough that the bread is not seen through the mayonnaise.
Sprinkle rehydrated onions over the mayonnaise.
Cover with Swiss cheese
On the other half of the bread, place cheddar cheese.
Please a slice of pepperoni on top.