Preheat oven to 450F. Lightly mist with cooking spray a baking dish just large enough to hold fish fillets in a single layer.
Place fillets in baking dish and sprinkle with salt and pepper.
Whisk olive oil, lemon juice and garlic in a small bowl and drizzle over fish.
Bake until fish is cooked through and no longer translucent, 7 to 10 minutes.
While fish is cooking, melt butter in a small pan until foamy. Stir in tarragon and capers. With a spatula, transfer cooked fish to plates and spoon butter sauce on top.