First, make the marinade. Place all the marinade ingredients in a blender and blend on high speed until smooth. Place the cubed tofu in a container, pour in the marinade, and refrigerate for at least an hour or overnight. The tofu will become more flavorful the longer it marinates.
When ready to cook, thread skewers with marinated tofu, pineapple, and red pepper in an alternating fashion–three pieces of each ingredient per skewer works well. Repeat until all the ingredients are used up. Reserve the extra marinade for brushing on the skewers while cooking.
To cook, preheat a grill or grill pan until hot. Brush with oil, then immediately place the prepared skewers on the grill. Brush each skewer with some of the remaining marinade, then cook for 3 to 5 minutes per side, basting each side with more marinade, until nicely browned and heated through. Serve immediately.