Ham Tetrazzini

Bring a large pot of lightly salted water to a boil.

Add spaghetti and cook for 8 to 10 minutes or until al dente; drain (or use leftover pasta; see Cook's Note).

While pasta is cooking, melt butter in a saucepan over medium heat.

Stir in onion; cook and stir until the onion has softened and turned translucent, about 5 minutes.

Stir in cream of mushroom soup, 1/2 cup water, and shredded cheese.

Heat mixture until cheese melts, stirring often.

Mix in the ham, cooked and drained pasta, chopped pimento, and chopped parsley to saucepan; stir to combine.

Cook until mixture is heated through, then serve.