Press out the water from the tofu. Cut the tofu into 3 even slices (about 3/4" thick).
In a large shallow dish, combine all the remaining ingredients. Add the tofu to the dish, ensuring the tofu is completely submerged in the marinade. Place in the refrigerator to marinate for 2 hrs.
Preheat grill. Once the grill is hot, carefully remove the tofu from marinade, reserving the marinade for later, and place the tofu on a non-stick grill mat on the grill.
Grill tofu on each side for about 5 mins, until the sides are blackened and the tofu is cooked all the way through.
Remove tofu from the grill and brush on a generous coat of excess marinade. Serve over a bed of steamed fresh spinach and top with slices Piquillo peppers.