1. Flake fish in a medium bowl. Add 1/4 tsp. lemon rind, 1/4 cup lemon juice, 2 Tbsp. olive oil, 1/4 tsp. salt, and 1/4 tsp. pepper, tossing gently to coat.
2. Spread Basil Mayonnaise evenly on cut sides of rolls. Place lettuce and fish on bottom halves of rolls; top with onion, and cover with roll tops.