Cook pasta according to package directions. Drain. Keep warm.
Meanwhile, melt butter in 10-inch skillet until sizzling; stir in zucchini, red pepper, onion and garlic. Cook over medium-high heat until onion is softened (2 to 3 minutes). Remove zucchini mixture from skillet with slotted spoon; set aside. Reserve butter in skillet.
Toss chicken strips with taco seasoning in medium bowl. Add chicken to same skillet. Continue cooking, stirring occasionally, until chicken is lightly browned and no longer pink (5 to 7 minutes).
Add zucchini mixture and milk to chicken. Reduce heat to medium. Cook until heated through (2 to 3 minutes). Remove from heat.
Add cooked pasta and cheese. Serve immediately with sour cream, if desired.