Preheat the oven to 425°F (220°C). Line an 18x13-inch baking sheet with foil and place an oven-safe cooling rack on top; spray the rack with nonstick cooking spray and set aside.
In a shallow dish combine the finely chopped pecans, panko breadcrumbs, paprika, garlic powder, and a few grinds of black pepper; mix until evenly distributed.
In a small bowl stir together 1 tablespoon Dijon mustard, 1 tablespoon mayonnaise, and 1/2 tablespoon honey to make the initial honey mustard for coating.
Pound each chicken breast to an even thickness of about 1/2 inch using a meat mallet or heavy pan. Pat dry with paper towels and season both sides lightly with salt.
Brush the top side of one chicken breast with the honey-mustard mixture, then place the brushed side down into the pecan-panko mixture and press firmly so the crust adheres to the bottom.
Brush the remaining side of the chicken with more honey-mustard, season with salt, then turn and press into the pecan-panko mixture so both sides are well coated. Repeat to coat all breasts, adding extra pecan mixture to the tops as needed.
Arrange the coated chicken on the prepared rack with space between pieces. If desired, lightly spray the tops with olive oil cooking spray to encourage browning.
Bake in the preheated oven until the chicken reaches 165°F (74°C) in the center and the crust is golden, about 20–25 minutes; tent with foil if the pecans are browning too quickly.
Meanwhile, in a clean small bowl whisk together the remaining 1 1/2 tablespoons Dijon mustard, 1 1/2 tablespoons mayonnaise, and 1 1/2 tablespoons honey.
When chicken is done, drizzle each piece with the reserved honey-mustard mixture and serve warm. Optionally garnish with about 1 1/2 teaspoons chopped parsley.