Prepare the chicken: If the chicken breast is very thick, slice it horizontally to create two thinner cutlets, or pound it to about ½-inch thickness. This ensures even cooking.
Coat the chicken: Lightly brush the chicken breast on both sides with sunflower oil. In a shallow dish, combine the panko breadcrumbs, salt, crushed pepper, ¼ teaspoon black sesame seeds, and ¼ teaspoon white sesame seeds. Press the chicken firmly into the breadcrumb mixture, ensuring it's fully coated on both sides. Gently pat to make sure the crumbs stick.
Air fry: Preheat your air fryer to 375°F (190°C) for 5 minutes. Carefully place the breaded chicken in the air fryer basket in a single layer (cook in batches if necessary). Air fry for 12-15 minutes, flipping halfway through, until the chicken is golden brown, crispy, and cooked through. An internal temperature of 165°F (74°C) is ideal for chicken.
Rest and slice: Once cooked, remove the chicken from the air fryer and let it rest on a cutting board for 5 minutes before slicing it into strips. This keeps the chicken juicy.
Assemble the bowl: Serve the sliced chicken katsu over a bed of steamed rice (not included in ingredients). Arrange the thinly sliced cucumber next to the chicken. Sprinkle the remaining ½ teaspoon black sesame seeds and ½ teaspoon white sesame seeds over the chicken and cucumber.
Garnish: Squeeze fresh lemon juice over the chicken and cucumber. Garnish with finely chopped fresh parsley before serving.