Put the mustard and mayonnaise in a small bowl and season with salt and pepper. Mix by whisking.
Combine the panko crumbs, parmesan cheese, paprika, fine sea salt, ground black pepper, and onion powder in a medium-sized bowl.
Coat the chicken on both sides by dipping it into the mayo mixture.
After placing the chicken in the panko bowl, turn it over to coat the other side. Make sure the chicken is well covered in crumbs by pressing the panko onto it.
Arrange the chicken on a baking sheet covered with parchment paper, then mist it with olive oil spray.
Bake until the internal temperature reaches 165 degrees, 15 to 22 minutes.
Before serving, let the chicken rest for five minutes. Serve right away after adding 1 tablespoon of freshly chopped parsley and a fresh lemon.