Boil the pasta as normal, but just a little under cooked. Darin and set aside.
In a small skillet sauté the butter with the onions, and peppers until translucent.
Add cream of celery, tuna, mushrooms, pimentos, mayonnaise, salt and pepper. Mix until well combined.
In a greased 9x13 add a layer of cooked past on the bottom. Then add a layer of the mixture. Continue to alternate layers and mix as you go. This is the best way to ensure the mixture finds its way through the pasta. Or, you can add the mixture to the bowl of drained past and fold together. Then put it in the baking dish. Either way works.
Sprinkle the cheese over the top and bake at 350 degrees for about 30 minutes, or until nice and bubbly.
