Place chicken and cajun seasoning in a bowl or resealable plastic bag; toss or shake to coat. In a large skillet over medium heat, saute chicken in butter until almost tender, about 5-7 minutes. Add peppers, mushrooms and onions; cook and stir for 2-3 minutes. Reduce heat. Add cream and seasonings; heat through. Add linguine and toss; heat through. Sprinkle with parmesan cheese if desired.