In 5- to 6-quart Dutch oven, cook linguine as directed on package. Drain well; return to Dutch oven and cover to keep warm.
Meanwhile, in blender, place clam chowder, milk, 1/2 cup Parmesan cheese and the garlic; blend on medium speed until mixture is smooth. Set aside.
In 12-inch nonstick skillet or wok, heat oil over medium-high heat until hot. Add shrimp, mushrooms and onions; cook about 5 minutes, stirring frequently, until shrimp turn pink.
Stir in pepper flakes and soup mixture; cook until thoroughly heated. Stir in parsley. Salt and pepper to taste.
Pour over cooked linguine in Dutch oven; toss gently to coat. Top individual servings with shredded Parmesan cheese.