Cook the pasta according to package directions, omitting salt and fat. Drain pasta in a colander over a bowl, reserving 1/4 cup cooking liquid. Combine shrimp, onions, and garlic in a small bowl. Heat a large skillet over medium-high heat. Add olive oil; swirl to coat. Add shrimp mixture, and sauté for 4 minutes or until shrimp are done. Remove from pan; keep warm.
Reduce heat to medium. Add reserved cooking liquid, Parmigiano-Reggiano, half-and-half, cream cheese, and pepper to pan. Cook 2 minutes or until cheeses melt. Combine pasta, cheese mixture, and shrimp mixture. Sprinkle with parsley.