Cut steak into 2 pieces; sprinkle with salt and pepper. Coat in flour, using a mallet, pound flour into the meat. In large skillet, brown meat on both sides. Transfer to a shallow 1 quart baking dish coated with nonstick cooking spray.
In same skillet, saute onion in drippings until tender. Stir in remaining ingredients. Pour over meat. Cover and bake at 350 degrees for 1 1/2 hours, or until tender.