Season the turkey schnitzel with salt and ground pepper on both sides. Layer in a container with finely sliced garlic, fresh rosemary, and optionally sliced lemon, drizzling each layer with olive oil. Cover and refrigerate for 30 minutes.
Heat a grill or skillet to medium-high heat. Cook the turkey schnitzel without adding extra fat—the oil from the marinade is sufficient. Cook until the internal temperature reaches 74°C (165°F).