Preheat the oven to 375 degrees . Place the garlic heads on a baking sheet and bake until softened, about 35 minutes. Let cool slightly.
Meanwhile, in a saucepan, cook the pomegranate juice over medium heat until reduced to a thick syrup, about 20 minutes; transfer to a cup.
Slice off the tops of the heads of garlic and squeeze the roasted garlic from the cloves into a bowl; mash until smooth. Stir in the mayonnaise; season with salt and pepper.
Place a dollop of the garlic mayonnaise onto each cucumber slice, drizzle with the pomegranate syrup and garnish with mint.