Lay each breast between layers of plastic wrap. Carefully pound chicken out to 1/4" thickness. Remove top layer of plastic wrap. Place a slice of prosciutto on chicken, and top with gruyere. Roll chicken into a tight pinwheel using plastic to help. Twist both ends of plastic wrap in opposite directions to make a tight cylinder. Repeat until all 4 breasts are done. Refrigerate at least 30 minutes until chicken firms up.
In a shallow dish, place flour. In a second dish, beat eggs. In a third dish, place panko. Add salt and pepper to each dish and stir well. Add thyme, garlic and melted butter to panko and stir well.
Unwrap chicken rolls. Gently roll in flour, then tap off excess. Dip in egg on all sides, then roll in panko until well-coated. Place rolls in large casserole dish. Drizzle with olive oil. Bake at 350°F for 20 minutes until golden brown. Let rest 3-5 minutes. Slice each roll into 4 slices before serving. Serve with Roasted Chicken Jus (see recipe elsewhere on this site).