Bring a large pot of water to a boil and cook pasta for 7 - 8 minutes or until it's tender but still has a bite to it. Drain.
While pasta is cooking, heat andouille sausage in a skillet over medium heat. Add in kale and cook just until wilted, about two minutes. Transfer to a plate and set aside.
In the same pan, melt butter over medium heat. Whisk in flour. Slowly whisk in milk until mixture is smooth. Whisk in cheese and cook until melted. Whisk in Dijon mustard and cajun seasoning.
Slowly beat in a tablespoon of the hot milk mixture in with the egg to temper it. Slowly whisk the egg into the milk mixture. Stir in andouille sausage, kale, and onion. Mix well.
Pour macaroni and cheese into a 2 quart casserole dish.
In a bowl combine panko bread crumbs, garlic powder and olive oil. Sprinkle over the top of the macaroni and cheese. Bake in preheated oven for 20 - 25 minutes or until bubbly and the crust has turned golden. If you would like a bit more brown on the crust, turn on a broiler for a minute or two. Serve hot.