Me being Dominican this is one of the things that I hate about the cuisine here, they love everything salad but nothing spicy. When I eat sushi I would eat the wasabi by bunches while my friends would look at me with their eyes wide open "como dos medio pesos".
One thing that it is really spicy here are "los palitos cervezeros" in any Chimi, or hamburger stand in Santo Domingo or Santiago. In Santo Domingo I personally prefer the one from the KM.9 in the Independencia Avenue, the place is called "Parking Lot". Los palitos cervezeros may not break your mouth, but will get close to it.