In a small bowl, combine the chili powder, sugar, garlic powder, onion powder, salt and pepper.
Use a pastry brush to coat both sides of the bell peppers, onions and scallions with some of the oil, then sprinkle with a quarter of the spice mix. Pat the steaks dry with a paper towel, then brush with the remaining canola oil and season with the remaining spice mix.
Grill the steaks until grill marks appear and they start to char slightly, about 3 minutes per side for medium rare. Grill the peppers, onions and scallions until grill marks appear, 3 to 4 minutes per side. Remove everything to a cutting board. Coarsely chop the vegetables first to allow the steaks some time to rest. Slice the steaks against the grain into thin slices.
Serve with the warm flour tortillas (I like to wrap a stack of tortillas in foil and warm on the grill) and sour cream, lettuce, guacamole, cheese and lime wedges.