Preheat charcoal grill or broiler.

In a large bowl, combine olive oil, Italian seasoning, salt and pepper. Lightly brush both sides of each bread slice with oil mixture; set aside.

To remaining oil in bowl, stir in mushrooms, red pepper and onion; toss to coat thoroughly. Place vegetables on a grill rack or broiler pan. Grill or broil, 4 inches from heat source until vegetables are lightly charred, 5 to 6 minutes, turning occasionally; remove and keep warm.

Place bread slices on the grill rack or under the broiler until lightly browned, about 30 seconds; turn bread. Sprinkle 1 cup of the mozzarella over bread slices, dividing evenly; heat just until melted. Top cheese with hot grilled vegetables and remaining 1/2 cup mozzarella.