Preheat oven to 425° F.
On a plastic wrap covered cutting board, place chicken thigh one at time and butterfly, then pound into a very thin fillet. Pat dry and season with salt and pepper.
In a baking dish whisk together eggs, milk, salt, and pepper.
In another baking dish combine breadcrumbs, cheese, onion powder, rosemary, and paprika.
One at a time, dip a piece of chicken in the egg and then cover and press with the breadcrumb mixture. Transfer to a plate to prepare for frying.
In a large sauté pan, heat up oil over medium-high heat. Cook chicken 4-5 minutes on a side or until golden brown and transfer to a greased baking sheet.
Top each piece of chicken with a generous spoonful of marinara sauce and 2-3 slices of fresh mozzarella.
Cook for 5-10 minutes until cheese is slightly golden and melted.