Brown beef in large skillet on medium-high heat. Drain fat.
Stir in Seasoning Mix, tomatoes and cheese. Cover. Cook on medium heat 3 minutes or until cheese is melted, stirring occasionally.
Stir in sour cream. Cook 3 to 5 minutes longer, stirring occasionally. Garnish with chopped fresh cilantro and chopped jalapeño peppers, if desired. Serve with tortilla chips.