In a medium bowl combine 1 tablespoon of the olive oil, the lemon juice, chives, basil, mint, and garlic. Add crabmeat, shrimp, tomatoes, and onion; toss to coat.
Cut bread into 48 thin slices. Arrange bread slices on a large baking sheet. Brush one side of each slice with some of the 2 tablespoons olive oil; sprinkle lightly with pepper. Broil 3 to 4 inches from heat for 1 to 2 minutes per side or until toasted.
To serve, spoon seafood mixture onto the oiled side of each toasted slice. If desired, garnish with fresh mint. Serve immediately. Makes 48 appetizer servings