Start by preheating your oven to 400°F (200°C). Take the boneless skinless chicken breast and place it between two sheets of plastic wrap. Using a meat mallet or rolling pin, gently pound the chicken to about 1/2-inch thickness for even cooking.
Sprinkle both sides of the chicken breast with salt. Set up a breading station with three shallow bowls: one with all-purpose flour, one with the beaten egg, and one with panko breadcrumbs. Dredge the chicken first in flour, shaking off any excess, then dip it in the beaten egg, and finally coat it in panko, pressing gently to adhere the breadcrumbs.
Place the breaded chicken on a baking sheet lined with parchment paper. Lightly spray the top with cooking spray to encourage browning. Bake for 20-25 minutes, or until the chicken is golden brown and cooked through, with an internal temperature of 165°F (75°C).
While the chicken is baking, prepare the pineapple katsu sauce. In a small saucepan over medium heat, whisk together the soy sauce, cornstarch, granulated sugar, brown sugar, white vinegar, pineapple juice, and ketchup. Stir continuously until the mixture thickens and bubbles, about 3-5 minutes. Remove from heat and set aside.
Once the chicken is done baking, remove it from the oven and let it rest for a few minutes. Slice the chicken katsu into strips and serve it over a bed of white steamed rice if desired. Drizzle with the pineapple katsu sauce and garnish with pineapple chunks for extra flavor and presentation.
