Trim any excess fat from the chicken breasts and cut them into serving-size pieces.
In a medium bowl, whisk together the egg and lemon juice until combined, then add the chicken pieces and toss to coat. Cover and refrigerate for 30 minutes.
Preheat the oven to 400°F (200°C). Line a baking sheet with parchment paper or foil and set aside.
In a shallow dish, combine the breadcrumbs, grated Parmesan, lemon zest, garlic powder, salt, and black pepper; mix well.
Remove the chicken from the egg mixture and dredge each piece in the breadcrumb mixture, pressing to adhere and coating both sides. Place coated pieces on the prepared baking sheet.
Lightly spray the tops of the coated chicken with cooking spray, then bake for 15 minutes. Flip each piece, spray again if desired, and bake an additional 10 minutes, until golden brown and cooked through.
Serve hot with fresh lemon slices.