In a large skillet, cook steak in canola oil over medium-high heat for 3-4 minutes on each side or until meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°). Add 1 tablespoon soy sauce, salt and pepper; cook 1 minute longer. Remove from the pan and keep warm.
In the same skillet, saute the mushrooms, onion and pepper in olive oil until tender. Stir in remaining soy sauce. Remove from the heat; add tomato. Spread mustard over rolls. Slice steak; place on rolls. Add mushroom mixture; replace tops.