Mix well the Herdez Tomatillo Sauce with the Sour Cream. Set aside.
Saute onions until clear, add roast beef and until tossed together well. Turn off stove.
Add 3/4 to 1/2 cup of the mixture starting at the end of the tortilla. Pour 1 T of the sour cream sauce over mixture. Roll tortilla from end where mixture is over and tuck. Fold sides of tortilla over middle. Roll to the end. Place on a cookie sheet. Continue until tortillas run out or the mixture does.
Generously coat Chimichangas with Extra Virgin Olive Oil over tops. Place in oven and bake until tortillas are browned and crispy.