You can also tenderize the flank steak with a meat mallet. Preparation: Preheat oven to 350 F. In a large frying pan over medium-high heat, saut the onions and mushrooms until tender; remove from heat an let cool.earch What's Cooking America. This delicious Stuffed Flank Steak recipe was shared with me my by Dina Calanchini of Sacramento, CA. Dina belongs to a Ladies Dinner Group in the Sacramento area, and they have lots of fun creating and cooking many different types of foods.