Marinate the Chicken:
In a mixing bowl, whisk together all marinade ingredients until well combined.
Place the chicken breasts in a resealable plastic bag or shallow dish and pour the marinade over them. Seal or cover, and refrigerate for 2–3 hours or overnight for best results.
Prepare the Ranch Spread:
In a small bowl, mix together the grated Parmesan cheese and ranch dressing until smooth. Set aside.
Prepare the Parmesan Crumb Topping:
In another bowl, combine the panko bread crumbs, garlic salt, shredded Parmesan cheese, and melted butter. Mix until the crumbs are evenly moistened. Set aside.
Cook the Chicken:
Preheat a grill or grill pan over medium-high heat.
Remove the chicken from the marinade and discard the marinade. Season both sides of the chicken breasts with salt and freshly ground black pepper.
Lightly oil the grill grates or grill pan. Grill the chicken for 6–7 minutes per side, or until the internal temperature reaches 165°F (74°C).
Transfer the cooked chicken to a baking sheet.