Heat oven to 350°F. In 12-inch ovenproof skillet, heat oil over medium-high heat. Add beef and onion; cook 6 to 8 minutes, stirring occasionally, until brown. Drain, and return mixture to skillet. Stir in taco seasoning mix and water. Cook over medium heat 2 to 3 minutes longer or until thickened. Transfer to medium bowl. Clean out skillet; spray with cooking spray.