In a mixing bowl, whisk together the lemon juice, crushed garlic (or garlic powder), onion powder, olive oil, kosher salt, black pepper, and Italian seasoning until combined.
If using whole chicken breasts, place them between plastic wrap and gently pound with a rolling pin or meat mallet to an even thickness for uniform cooking.
Place the chicken in the bowl or a shallow dish and pour the marinade over it, turning to coat evenly. Let the chicken marinate for 15–30 minutes.
Preheat your grill or griddle to medium-high and lightly oil the cooking surface.
Grill the chicken, turning once, until cooked through and no longer pink in the center (about 4–7 minutes per side, depending on thickness) and juices run clear.
Transfer the chicken to a plate, let rest briefly, then garnish with chopped fresh parsley and serve warm or at room temperature.