1. Preheat oven to 450°.
2. Spray a small baking dish with cooking spray; add halibut and season with a pinch each salt and pepper; rub with 1 teaspoon oil. Bake 10-15 minutes, until cooked through and the flesh flakes easily with a fork. Cool.
3. Remove some bread from top half of loaf. Brush cut sides with 2 tablespoons olive oil. Bake on a baking sheet 6-8 minutes, until golden. Rub toasted surfaces with garlic.
4. In medium bowl, combine mayonnaise, sun-dried tomatoes, basil, parsley, capers, and lemon zest. Add fish, flaking and mixing with fork. Spoon onto bottom half of bread and top with arugula. Add top of bread and cut into 4 sandwiches.