POKE holes all over tofu with a skewer. Pat dry with paper towels and cut into 3/4-in. cubes. Whisk coconut milk, curry paste, brown sugar, peanut butter and soy sauce in a medium bowl. Add tofu and toss to coat. Set aside to marinate for 1 hr.
PREHEAT barbecue to medium. Shake excess marinade off tofu and back into the bowl. Divide marinated tofu and thread onto skewers.
SCRAPE marinade into a small saucepan and set over medium-high. Cook, stirring often, until mixture reduces by half, 5 to 6 min. Set aside.