Healthy twist on a classic favorite.
To cook the spaghetti squash in Instant Pot - puncture squash several times.
Place steam rack in pot and add 1 cup of water. Place squash on steam rack.
Set to high for 20 minutes for a 4-5 pound squash. Look up cook time for a smaller squash. When done, use manual release and remove squash from pot so that it doesn't keep cooking.
Let squash cool enough to handle. When cooled cut in half and remove seeds.
Preheat oven to 400 degrees. While squash is cooking, cook onions until translucent.
Remove squash from shell and add to large mixing bowl.
Stir in onions, peas, mushrooms, tuna, cheese and salt and pepper. Combine well.
Top with bread crumbs and sprinkle more Parmesan on top. I like to spray lightly with cooking spray so the topping isn't dry.
Cook casserole for 20 minutes, making sure it's heated all the way through.
Broil for the last few minutes to brown the top.