Cook fettuccine according to package directions.
Meanwhile, melt butter in 12-inch skillet over medium heat.
Add carrots; cook 3 minutes, stirring occasionally.
Add zucchini and shrimp; cook 5 minutes or until shrimp are opaque and vegetables are crisp-tender, stirring occasionally.
Add sausage; cook 2 minutes, stirring occasionally.
Add half-and-half, ¾ cup Parmesan cheese and Cajun seasoning; heat through, stirring constantly.
Drain pasta; return to pot. Add shrimp mixture; toss well.
Transfer to serving platter; sprinkle with remaining Parmesan cheese and additional Cajun seasoning, if desired.