Preheat the oven to 350°F and grease a 2-quart casserole dish.
Bring a large pot of salted water to a boil.
Divide the pasta dough into 2 equal portions. Using additional tapioca starch as needed to avoid sticking, roll out the dough to roughly ¼ inch thick. Use a pizza cutter or knife to cut into
noodles roughly ½ x 2 inches.
Boil the noodles for 7 minutes, drain, and rinse with cold water. Set aside. (The noodles should be al dente.)
In a large-size skillet over medium heat, melt the fat. Cook the mushrooms, onion, and garlic until soft, about 3 minutes. Stir in the arrowroot starch. Add the peas, tuna, and roughly 1/2 of
the Parmesan cheese, mix well, and cook until heated through, about 2 minutes.
Slowly stir in the half-and-half, heat to a simmer, and cook for 2 to 3 minutes, or until slightly thickened. Season with salt and pepper. Remove from the heat and fold in the noodles.
Transfer the mixture to the prepared casserole dish, cover with foil, and bake for 15 minutes, until heated though. Remove from the oven, top with the remaining Parmesan cheese and the Cheddar cheese, return to the oven, and bake for an additional 5 minutes, or until the cheese is melted.
Allow to rest/cool for 5 minutes prior to serving. Enjoy!