Preheat oven to 425°F.
Coat a small baking pan with cooking spray.
Combine breadcrumbs, garlic and oil in a small bowl.
Combine yogurt, mayonnaise, lemon juice, tarragon and salt in another small bowl.
Place fish on the prepared baking pan.
Spread 1 tablespoon of the yogurt sauce on each piece of fish, then pat 2 tablespoons of the breadcrumbs over it.
Bake the fish until opaque in the center and the breadcrumbs are golden, about 15 minutes.
Serve each portion with 1 tablespoon of the remaining sauce and a lemon wedge