Cook pasta according to package directions, omitting salt and fat.
Drain.
While pasta cooks, melt margarine in a large nonstick skillet over medium-high heat.
Add green onions, lemon juice, and garlic; cook 2 minutes, stirring often.
Add shrimp, and cook 5 minutes or until shrimp turn pink.
Remove shrimp from skillet; set aside.
Add half-and-half, cream cheese, and dill to skillet, stirring until smooth. Cook 1 to 2 minutes or until mixture is bubbly. Return shrimp to skillet, and cook until thoroughly heated.