MUSHROOMS: Heat oil in a large nonstick skillet over medium-high heat. Add onion, shallots, and garlic to pan; sauté 3 minutes or until tender. Add mushrooms; sauté 5 minutes or until mushrooms are tender. Add wine, oregano, 1/4 teaspoon salt, and 1/4 teaspoon pepper; cook 2 minutes or until liquid evaporates. Set aside.
SAUCE: Melt butter in a large saucepan over medium-high heat. Add flour to pan; cook 2 minutes, stirring constantly. Add milk and broth, stirring with a whisk until smooth; bring to a boil. Cook 2 minutes or until thick, stirring constantly with a whisk. Remove from heat. Add cheese, remaining 1/4 teaspoon salt and remaining 1/4 teaspoon pepper; stir until smooth. Stir in mushroom mixture. Keep warm.
PASTA: Cook pasta according to package directions. Fold mushroom-sauce mixture into pasta and garnish with parsley, if desired. Serve immediately.