Thaw shrimp, if frozen. Rinse shrimp; pat dry with paper towels. Set shrimp aside. Cook fettuccine according to package directions; drain and return to pan. Toss with 2 tablespoons of the olive oil. Cover and keep warm.
Meanwhile, in an extra-large skillet heat the remaining 2 tablespoons oil over medium-high heat. Add sweet peppers, onions, and garlic; cook and stir for 4 to 6 minutes or until crisp-tender. Add shrimp and cayenne pepper. Cook and stir for 2 to 3 minutes or until shrimp are opaque. Serve shrimp mixture over pasta.