Chicken and Grilled Vegetable Sandwich

4 pieces focaccia bread, sliced in half crosswise

1/3 cup butter, softened

1 cup chicken bacon spread

1 large red bell pepper, grilled or roasted and sliced into strips

1 medium onion, sliced into rings and grilled

1/2 cup fresh button mushrooms, grilled or sautéed

flat-leaf parsley, for garnish