In a large pot, cook spaghetti, al dente, according to package directions. Drain but do not rinse.
In a large skillet over medium heat, melt the butter.
Add the onion and sliced mushrooms. Cook, stirring occasionally, until the onions are soft and the mushrooms are lightly browned.
Stir in the cream of mushroom soup, milk, salt, and pepper.
Mix well.
Add the ham, peas, roasted red peppers, and both cheeses.
Lower the heat to medium and cook until the cheese is melted and sauce heated through and peas are softened.
Add in the cooked pasta and stir to coat the pasta in the sauce.
Garnish with fresh chopped parsley. Serve warm and enjoy.