In a medium bowl, combine shrimp with oil and 1 tbsp (15 mL) seasoning (4 tbsp (60 mL) for 24 servings); marinate for 30 minutes.
In a medium pan on medium-high heat, add butter and onions; cook for 2 minutes. Add mushrooms and sauté for 4-5 minutes. Add remaining seasoning, sauté for 1 minute. Add white wine and reduce until almost dry.
Add Alfredo sauce and milk; simmer for 10 minutes or until desired consistency, then add chives.
Preheat grill to medium-high heat. Grill shrimp approximately 2 minutes per side. Cook the pasta until al dente.
Serve pasta with 3/4 cup (175 mL) sauce per person and 4 shrimp.