Preheat the oven to 350. Prep a 2.5 quart casserole dish (or two smaller casseroles) with cooking spray or olive oil.

Start the water for the pasta and cook it while you make the sauce. Cook it the minimum time recommended as the pasta will finish in the oven. Drain it well and let it sit until you need to add it to the casserole.

Meanwhile, use a large saucepan or dutch oven, to saute the onions (and garlic if using) in the butter and olive oil.

When the onions have softened, sprinkle the flour over top and cook for a few minutes. It will clump up.

Add about half the chicken broth to the pot and stir well to break up any clumps. The sauce should smooth out and thicken up. Add more broth, eyeballing the amount needed to cover the type of pasta used.

Stir in the cheese and allow it to melt. The sauce should be nice and thick by this point. Taste and add salt and pepper as desired.

Add the tuna, peas, parsley and drained pasta. Mix well.

Taste again and adjust the seasoning.

Pour into casserole dishes, top with bread crumbs and bake for 20 - 25 minutes until the casserole is bubbly and the topping starts to brown.