In a large bowl, combine buttermilk, garlic powder, onion powder, paprika, salt, and black pepper. Add the chicken breasts, ensuring they are fully submerged. Cover and refrigerate for at least 1 hour or up to overnight for maximum flavor and tenderness.
Preheat your oven to 400°F. Line a baking sheet with parchment paper.
In a shallow dish, combine flour, panko breadcrumbs, and grated Parmesan cheese. Remove the chicken from the buttermilk marinade, allowing excess to drip off, then dredge in the breadcrumb mixture, pressing gently to adhere.
Heat a large skillet over medium-high heat and add enough olive oil to cover the bottom. Once hot, add the breaded chicken breasts and cook for about 4-5 minutes on each side, until golden brown and cooked through. Transfer the chicken to the prepared baking sheet and bake in the oven for an additional 10 minutes to ensure they are crispy.
While the chicken is baking, prepare the Caesar dressing by whisking together mayonnaise, lemon juice, Worcestershire sauce, and a pinch of salt in a small bowl.
To assemble the sandwiches, spread a generous amount of the Caesar dressing on one side of each slice of bread. Layer with crispy chicken, chopped romaine lettuce, and cherry tomatoes. Top with extra Parmesan cheese, then close the sandwich with the other slice of bread.
Serve immediately and enjoy your delicious Crispy Chicken Caesar Sandwich!