HEAT grill to medium heat.
BRUSH mushroom and pepper with reserved artichoke marinade. Grill 5 min. on each side, brushing with any remaining marinade for the last few minutes.
MEANWHILE, grill bread 1 to 2 min. on each side or until lightly toasted on both sides.
SLICE mushroom and pepper. Spread 1 toast slice with dressing; spread remaining toast slice with pesto. Fill toast slices with grilled vegetables, cheese and artichokes to make sandwich.