BLEND milk, cream cheese and hot sauce in blender until well blended. Cook spaghetti as directed on package.
MEANWHILE, heat oil in large skillet on medium heat. Add onions; cook and stir 5 min. Add remaining vegetables; cook and stir 8 min. or until crisp-tender. Stir in cream cheese mixture; cook 5 min. or until heated through, stirring frequently.
DRAIN spaghetti; place in large bowl. Add 3/4 cup cheddar and 1/2 the herbs; toss until melted. Top with vegetable mixture, remaining cheddar and herbs.