Preheat your oven to 350°F (175°C).
Mix the tuna, celery, apple, walnuts, and shredded cheese in a large bowl.
Add the cooked macaroni and mayonnaise, ranch dressing, and Dijon mustard.
Stir everything together until well combined and evenly coated in the creamy dressing.
Transfer the mixture to a greased casserole dish.
Bake uncovered for 30 minutes or until bubbly and lightly golden on top.
Remove from the oven and let it sit for a few minutes before serving.