Cook pasta by following instructions on packaging. Meanwhile the pasta is cooking carry on with the rest.
Heat oil or butter in a pan and saute diced onion with salt on high heat until glassy / translucent look for about 5 minutes
Add diced celery and carrots and saute them for 5 more minutes then turn the heat to medium and cook it for 5 more minutes.
Add sliced mushrooms and stir fry until the mushrooms collapse about half of their size for about 5 minutes. Add peas and stir fry it for 5 - 7 more minutes. Frozen peas needs a bit more time to get ready but about 10 minutes it should be ready to go.
Mix in cream, pasta tuna then pour everything into a casserole dish.
Sprinkle grated cheddar and Parmesan on top. Some like to add breadcrumbs or panko on top as well but apart from added calories this step has neither nutritional value nor any other advantages of developing additional flavors or texture.
Put it under the broiler on maximum heat until the cheese gets a golden brown color for about 10 - 15 minutes.