Mix or whisk together: steak sauce, soy sauce, garlic, paprika and balsamic vinegar.
Brush this on top of the Portobello pieces, and marinade for about 15-20 minutes.
Heat oil on stove top on medium heat.
Add in Portobello and cook on each side for about 5 seconds or until it shrinks down and darkens.
*Picture: served w/ chimichurri & mashed potatoes!