Gather all ingredients.
Preheat the oven to 400 degrees F (200 degrees C).
Pat chicken dry with paper towels. Season both sides evenly with salt and pepper.
Finely chop white parts of scallions to measure 2 tablespoons; place in a small microwavable bowl with butter and microwave on High, stirring occasionally, until melted, for 1 minute. Thinly slice dark green parts of scallions to measure about 2 tablespoons and set aside. Add to melted butter and microwave for 1 more minute, stopping to stir occasionally.
Stir together panko, Parmesan cheese, cayenne, and paprika in a small bowl until well combined. Drizzle with butter mixture and stir together until panko is moistened and evenly coated.
Use the back of a spoon to spread ½ tablespoons Dijon mustard over top and sides of each chicken thigh.
Carefully sprinkle 2 to 3 tablespoons panko mixture over mustard coating on top and sides of each chicken thigh; gently press to adhere. Arrange chicken on a rimmed baking sheet about 1 ½- to 2-inches apart.
Bake in the preheated oven until chicken is no longer pink in the center, juices run clear, and panko mixture is golden brown, 40 to 45 minutes. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C). Remove from oven, let stand for 5 minutes, and serve warm.
