In large bowl, combine tomato sauce, chili powder, cumin and oregano leaves. Place ½ cup enchilada sauce in bottom of a 13x9-inch baking dish. Set aside.
In large skillet, cook and crumble beef and onions until no longer pink; drain. Add 1 cup enchilada sauce and 1½ cups cheese to beef. Divide among warmed tortillas and roll up; place seam-side-down in baking dish.
Pour remaining sauce over tortillas; top with remaining cheese. Bake in a preheated 375°F oven 30 minutes or until cheese is melted and bubbly.