This is a great appetizer because of its big two-level crunch. First, the happy pop of the tobikko, and then the satisfying crunch of the crostini.
To make the ahi spread, combine all the ingredients (ahi, tobikko, green onion, soy sauce, wasabi, kosher salt, and black pepper) in a bowl, fold together, and keep well chilled until ready to serve.
To make the crostini (you can also purchase prepared crostini), brush each slice of bread with a little olive oil and bake at 400° F for 10 minutes or until crispy. Remove from the oven and sprinkle with garlic salt or a herbed salt blend.
Top each crostini with a rounded teaspoon of the ahi spread and serve.