SAUCE: Mix all sauce ingredients well, cover and set aside.
POTATOES: Heat oil in a skillet to 350°F Add sliced potatoes and fry, turning occasionally, until done (about 7-10 min). Drain potatoes on paper towels, and sprinkle lightly with salt.
ROLLS: To the pan with oil, reduce heat to medium and add the butter. When melted, add the garlic and cook 2-3 minutes until garlic is tender.
Place the cut side of the rolls face down into the garlic butter. Press gently to coat. Place rolls onto a baking sheet, butter side up. Broil in oven or toaster oven until nicely browned and toasted. Remove from broiler and set rolls onto plates. Add a slice of Swiss cheese to the bottom bun.
VEGETABLES: To the pan over medium-high heat, add the peppers and onions. Cover and let steam 2-3 minutes. Remove lid, stir, and continue cooking until onions are translucent and peppers done. Place vegetables in a dish and set aside.
MEAT: To the pan add a bit more olive oil and butter if necessary. (enough to sear steak). Add seasoned steak and let sear for 2-3 minutes. Toss and continue searing until almost desired doneness. Add mushrooms to pan and saute' for 2-3 minutes until mushrooms are browned and flavored with the meat juices. Drain meat and mushrooms onto a paper towel.
ASSEMBLY: To each bottom bun, add the meat, then vegetables, then potatoes. To the top bun, spread with sauce and place over top. Grab lots of napkins, a fork (to catch what falls on the plate), and enjoy.
ALTERNATIVE: Wrap sandwich in foil and eat 'to go' style.