Heat oil in large deep skillet on medium-high heat. Add chicken and 1 tbsp. of the Seasoning Mix; cook and stir 5 minutes or until browned. Remove chicken. Add onion to skillet; cook and stir 3 minutes or until softened.
Add stock, tomatoes and remaining Seasoning Mix to skillet; bring to boil, stirring to release browned bits from bottom of skillet. Stir in pasta. Cook 15 to 20 minutes or until pasta is tender, stirring occasionally.
Return chicken to skillet. Stir in mozzarella. Cook 2 minutes or until chicken is heated through.