To make the chipotle mayonnaise: Combine the mayonnaise, whole grain dijon mustard, chipotle chiles and white wine vinegar in a small bowl and whisk to combine. Season with salt and pepper to taste and set aside. Chipotle mayonnaise can be made 3 days in advance and stored in the refrigerator.
For the steak, blot dry with a paper towel. Season with salt and pepper. Grill steak for 3-4 minutes per side over a medium high fire for a medium rare steak (130 - 135 degrees, internal temperature). If you like your steak more well done, cook for an additional 1 - 2 minutes (140 - 145 internal temperature). Remove steak from grill and let rest for 5 - 10 minutes.
While steak is resting, heat a skillet over medium high heat and add the olive oil. Add the onions and the mushrooms and saute until mushrooms are browned and onions are tender - about 4- 5 minutes. Add the sherry wine vinegar and stir to loosen any browned bits on the bottom of pan. Continue to cook until the vinegar evaporates, about 1 minute. Set aside.
Slice steak and assemble the sandwich.
Spread a layer of mayonnaise on the bottom of the Talera roll. Top with about 2 Tbsp. of the arugula. Place about ¼ of the steak slices on top of the arugula and top with ¼ of the red onion and mushroom mixture. Add the top of the roll and repeat with the remaining rolls and sandwich fillings and serve!