In a shallow dish, combine the buttermilk, garlic powder, onion powder, salt, and pepper. Add the chicken breasts, ensuring they are well-coated. Cover and refrigerate for at least 30 minutes.
Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper for easy cleanup.
In a separate bowl, mix breadcrumbs with grated Parmesan cheese. Remove the chicken from the marinade and dredge each breast in the breadcrumb mixture.
Heat olive oil in a large skillet over medium heat. Cook the coated chicken breasts for about 5-7 minutes per side, or until golden brown. Alternatively, bake for 20-25 minutes until crispy.
Slice the sandwich buns and toast them lightly. Spread Caesar dressing on both halves. Layer chopped romaine lettuce, followed by the crispy chicken breast, and drizzle more dressing on top.
Place the other half of the bun on top to finish off the sandwich. Serve immediately while the chicken is hot and crispy.