In medium saucepan, combine water and salt. Bring to a boil. Stir in rice; cover. Remove from heat; let stand 5 minutes.
Meanwhile, cut beef into 1/4-inch-thick strips; cut strips into 1-inch pieces. In medium bowl, combine beef pieces, taco seasoning mix, lime juice, oil, garlic and red pepper flakes; toss to coat.
Spray large wok or 12-inch skillet with nonstick cooking spray. Heat over medium-high heat until hot. Add beef mixture; cook 4 to 5 minutes or until beef is browned.
Stir in cooked rice, beans and corn; cook 4 to 5 minutes or until thoroughly heated, stirring occasionally. Add spinach; cook just until spinach begins to wilt. Garnish as desired.