Preheat oven to 400°F. In large bowl, gently toss bread cubes with 1 Tbsp oil. Season with salt and black pepper. Arrange bread in single layer on baking sheet. Bake 10 min. Transfer to sprayed baking dish, sprayed with cooking spray.
In large skillet over med-high heat, add oil and heat till hot. Add onions, red peppers and mushrooms. Cook 5 min. Add cubed chicken, cook 5 min or until browned. Stir in Italian herbs, crushed tomatoes, and vinegar. Increase heat to high, bring to boil. Reduce heat to medium, simmer 5 min.
Spoon chicken mix over bread in casserole dish. Top with Kraft Mozzarella Cheese and sliced tomatoes. Bake 15 min or until heated through.