Cook the noodles, just until al dente
Melt 1 tbsp butter in a large skillet. Add celery, onion, peas, and garlic. Sauté for a few minutes, then remove vegetables from the pan and set aside.
Add 3 tbsp butter to the pan. Once the butter is melted, add the flour and cook, stirring for 30 seconds. Slowly whisk in the chicken broth and milk, stirring constantly until smooth.
Bring the mixture to a low simmer and stir constantly, until thickened and bubbly. (2 to 3 minutes) Reduce heat to low, and add salt, dill, lemon juice, parsley, and 1/2 cup Parmesan cheese. You can add additional salt, pepper, or lemon juice, to taste.
Remove the mixture from heat, and stir in the pasta, vegetables and tuna. Pour into a 9x13 or similar baking dish, and sprinkle wit the remaining 1/2 cup Parmesan cheese.
Add melted butter to the crushed Ritz crackers. Sprinkle over the casserole.
Bake at 350 F for 25-30 minutes.