Preheat the oven to 400˚F (204˚C). Line a baking sheet with parchment paper.
In a small microwave-safe bowl, combine the guava paste slices and water. Microwave for 30 seconds or until soften. Stir with a fork and break up the guava paste until spreadable (lumps are ok). Set aside.
Place the bread slices on the baking sheet. Lightly brush the top with olive oil. Bake in the oven for 5 minutes. Remove from oven and place 2 slices of cheese on top. Back in the oven for 4 minutes. Remove from oven and dollop about a teaspoon of guava mixture on top. Return to oven to bake for another 2 minutes. Remove from oven and transfer to a serving plate. Serve immediately.