In a bowl, mix the chili powder, cumin and coriander. Set aside. Place the pork, peppers and onion in a baking dish. Rub all with the garlic seasoning paste, then sprinkle with the spice mixture, patting a generous amount on the pork. Cover and refrigerate for 30 min. or up to 24 hrs.
Heat barbecue to medium high. Grill pork 20 to 25 min., turning and brushing with barbecue sauce at least twice. Reduce heat to low and add peppers and onion, cooking 10 to 15 min. or until softened and lightly charred.
Remove peppers and onion, slice peppers into strips. Remove pork and let rest 5 min. before slicing thinly. Season pork and vegetables with salt. Warm tortillas on grill about 30 seconds per side. Serve with your favourite toppings, such as salsa, sour cream, guacamole, chopped tomatoes, cilantro and lime wedges.