Heat gas or charcoal grill. In small microwavable bowl, microwave cream cheese on High 15 to 20 seconds; stir until creamy. Stir in pesto and butter until well mixed.
When grill is heated, place bread pieces, cut side down, on gas grill over medium heat or on charcoal grill over medium coals. Cook 1 to 2 minutes or until lightly browned.
Turn bread halves over. Spread pesto mixture evenly on cut sides of bread; cover grill. Cook 3 to 4 minutes or until thoroughly heated. Cut bread into 2-inch sections to serve. Garnish with tomatoes.