Combine all the ingredients for Tikka masala in a large mixing bowl. Add the tofu, peppers and onions. Mix well, cover and set aside for at least 30 minutes and for up to 2 hours.
Soak the skewers in water for 20~30 minutes.
Thread the marinated tofu and veggies on to the skewers.
Heat the grill on medium heat. Lightly grease it with cooking spray. Grill the skewers until nicely grilled on all sides. Serve hot.