Preheat the oven to 375 F and grease a 2 quart casserole dish with butter or non stick spray. 

Bring a large stock pot of salted water to a rolling boil. Add pasta and cook for 8-10 minutes or until al dente according to package directions.

In a large skillet heat olive oil on medium heat. Add in celery, yellow onion and carrots and sprinkle with salt and cracked black pepper. Cook for 5-6 minutes or until onions are translucent. Remove celery, yellow onion and carrots from skillet and into a bowl, set aside.

In the same skillet heat butter on medium heat until melted. Whisk in flour and cook for 1-2 minutes.

Slowly whisk in chicken broth and whole milk. Cook for 3-4 minutes, whisking constantly until mixture is thick enough to coat the back of a wooden spoon. Season sauce with garlic powder and a sprinkle of salt and cracked black pepper. 

In a large bowl toss together cooked noodles, carrot-celery-onion mixture, sauce, spinach leaves, frozen peas and drained can of Bumble Bee® tuna. Transfer to prepared casserole dish.

In a medium bowl crush the crackers. Stir crackers with melted butter, garlic powder and season with salt and cracked black pepper. Top the casserole evenly with cracker mixture and shredded cheese.

Bake the casserole for 15-20 minutes or until the top is golden brown and the cheese is bubbly.