1. Adjust oven rack to middle position and heat oven to 300°F. Set wire rack inside rimmed baking sheet and spray with vegetable oil spray. Melt butter in 12-inch skillet over medium heat. Add shallot and 1/2 teaspoon salt and cook until softened, about 3 minutes. Add garlic and thyme and cook until fragrant, about 30 seconds. Add panko and 1/4 teaspoon pepper and cook, stirring constantly, until evenly browned, 5 to 7 minutes. Remove from heat and stir in parsley. Transfer panko mixture to shallow dish and let cool for 10 minutes.

2. Whisk mayonnaise, egg yolk, lemon zest, and 1/4 teaspoon pepper together in bowl. Pat fish dry with paper towels and season with salt and pepper. Coat tops of fillets evenly with mayonnaise mixture. Working with 1 fillet at a time, dredge coated side in panko mixture, pressing gently to adhere, and place fish crumb side up on prepared wire rack. Bake until centers are just opaque and fish registers 135°F, 30 to 40 minutes, rotating pan halfway through baking. Serve.

Serves 4