Slice chicken breasts horizontally into thin cutlets.
In one bowl, whisk egg, milk, garlic powder, salt, and pepper. In another, combine breadcrumbs and Panko.
Dip chicken into egg mixture, then coat in breadcrumbs.
Fry in hot oil over medium-high heat for about 5 minutes until golden and crispy. Transfer to paper towels.
Mix all garlic butter ingredients in a bowl.
Slice bread and spread garlic butter inside. Toast in a 450°F oven for 3–4 minutes.
Whisk together all Caesar dressing ingredients until smooth.
Toss romaine lettuce with 3–4 tablespoons of dressing.
Assemble Chicken Caesar Sandwiches by layering crispy chicken, dressed lettuce, and extra Parmesan inside toasted bread.
Serve immediately and enjoy.