Combine panko, cornstarch, garlic powder, smoked paprika, and black pepper in a shallow dish, then coat each chicken cutlet evenly.
Heat avocado oil in a large skillet over medium-high heat until shimmering.
Cook the chicken cutlets for 5 to 6 minutes per side until golden and crispy, reaching 165°F / 74°C at the thickest part.
Transfer the chicken to a wire rack and rest for 5 minutes to keep the coating crisp.
Spread mayonnaise on the bottom bun, add lettuce, place the chicken cutlet on top, and close with the top bun.