Cook noodles of choice per package directions, omitting salt & fat. Drain and keep warm.
Preheat oven to 325 F. Spray a 2-quart baking dish with cooking spray and set aside.
While pasta is cooking, saute celery and mushrooms in butter over high heat 7 minutes; add peas and green onions and saute until mushroom liquid has evaporated, about 3 minutes. Stir in flour (may need to add a dab more butter or oil) and stir to blend. When bubbling, add milk and bring to boil, stirring constantly. Reduce heat to low and simmer, stirring constantly, until thickened, about 2 minutes. Remove from heat and add parsley, thyme, salt and cayenne pepper.
Layer noodles, sauce and tuna (broken up) to casserole. Crumble crackers, such as Ritz, Waverly Wafers or Club crackers (or saltines if that's what you have) over top and sprinkle with cheese. Bake 20 to 30 minutes until heated through and bubbling.
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