Stir in the frozen peas, cream of mushroom soup, milk, and chicken broth into the skillet. Heat the mixture until it begins to simmer, stirring constantly until the sauce thickens slightly.
Remove the skillet from the heat. Stir in the drained tuna, cooked pasta, dried parsley, and black pepper until everything is well combined in the creamy sauce.
If you used a saucepan, transfer the mixture to your prepared baking dish. Sprinkle the shredded cheddar cheese evenly over the top.
Mix the breadcrumbs with a drizzle of olive oil (optional) and sprinkle them over the cheese layer.
Bake for 15 to 20 minutes, or until the topping is golden brown and the sauce is bubbly.
Let the bake rest for 5 minutes before serving directly from the pan.
Notes
For a homemade white sauce instead of canned soup, melt 2 tablespoons of butter, whisk in 2 tablespoons of flour, then slowly whisk in 1 1/2 cups of milk until thick. Season with salt and pepper before adding to the skillet.
Use any short pasta shape you have on hand. This recipe works well with pantry staples.
To make this a Tuna Mornay variation, add a dash of nutmeg to the sauce base.