How to Make It
Combine chopped fennel, red onion, 1/4 cup basil, capers, lemon juice, olive oil, 1/4 teaspoon black pepper, tuna, and bell peppers in a bowl, stirring well. Spoon 1/2 cup tuna mixture on each of 4 bread slices. Top each serving with 1 bread slice. Cut each sandwich in half diagonally.