Preheat broiler. Place bread slices on large baking sheet; spray evenly with cooking spray.
Broil 1-2 minutes until golden brown; turn over. Spray with additional cooking spray; sprinkle with garlic salt. Continue broiling 1-2 minutes, or until second side is golden brown. Remove from baking sheet to wire rack. Cool.
Combine tomatoes, basil and onion in medium bowl. Spoon evenly onto bread slices just before serving