Slice the chicken breasts horizontally into 4-6 thin cutlets. Whisk together the egg and milk in a shallow bowl. Dip each cutlet into the egg mixture, then coat with seasoned breadcrumbs and panko. Heat vegetable oil in a skillet over medium heat until shimmering, and fry the chicken cutlets for about 5 minutes per side until golden brown and crispy. Set aside on paper towels.

Prepare the garlic butter bread by mixing softened salted butter, mayo, minced garlic, fresh parsley, and grated Parmesan until well combined. Split the hoagies or baguette lengthwise and spread the garlic butter mixture on the inside of each piece. Preheat the oven to 450°F and toast the bread on a baking sheet for 3-4 minutes until golden and fragrant.

Make the Caesar dressing by combining mayo, sour cream (or Greek yogurt), Parmesan, lemon juice, Dijon mustard, anchovy paste, Worcestershire sauce, and grated garlic in a medium bowl; whisk until smooth and creamy. Add salt and pepper to taste.

Chop and rinse the romaine lettuce and add 3-4 tablespoons of the Caesar dressing, tossing gently until evenly coated.

Assemble the sandwiches by taking the toasted garlic butter bread, layering with crispy chicken cutlets, topped with dressed romaine lettuce, and sprinkling additional Parmesan if desired. Close the sandwich and serve immediately.

Serve hot and enjoy with potato chips, waffle fries, or tater tots.