In a large bowl, toss potatoes with oil, garlic powder and Cajun seasoning, if using. Season with salt and pepper.
Place potatoes in basket of air fryer and cook at 400° for 10 minutes. Shake basket and stir potatoes and cook until potatoes are golden and tender, 8 to 10 minutes more.
Squeeze lemon juice over cooked potatoes and garnish with parsley before serving.