You'll need decent sized chicken breasts when you are planning to make this. It's best if you're able to create a pocket in the fillet to hold the garlic butter - this will result in a much moister chicken kiev!
Use a food processor to blitz the bread into breadcrumbs. Transfer to a flat plate and set aside.
Either by hand or in a food processor blend the butter, garlic, parsley and lemon juice until well combined. Season with salt and pepper. Transfer to a piece of plastic wrap, roll up and freeze for 5 or 10 minutes until hardened.
Make a slit in each chicken breast that creates a pocket. Divide the chilled garlic butter between the two chicken breasts, wrapping the chicken fillet around it. Dip into the beaten egg, turning it over to make sure it's well coated. Then cover with breadcrumbs.
Heat oil over medium-high heat, and brown the chicken, for about 2 minutes on each side. Transfer to oven-proof dish and cook for an additional 15 minutes or until cooked through.