SPRINKLE half of cheese over four tortillas. Top with tomato slices and remaining cheese. Press remaining tortillas on top.
SET large skillet over medium heat until hot. Place first quesadilla in skillet and cook until browned on underside, about 1 minute.
TURN with spatula and cook until quesadilla is browned on second side and cheese is melted, about 1 minute longer.
REPEAT with remaining quesadillas. (Keep cooked ones warm in 200°F oven if not serving immediately.)
CUT each quesadilla into eight pieces; top each with dollop of guacamole.
Recipe courtesy of Chef Jon Ashton.