Slice the onion and pepper into 1/8" wide pieces
Turn on the oven, and set it to 350F
Add oil to the 6" pan, turn heat to high, add the sliced onion and pepper to the pan, and stir. Once the pan becomes hot, add the wine (water), and cover the pan with a lid. Turn heat to low to medium
Stir the veggies every 3 minutes. After about 15-18 minutes, both pepper and onion become tender. Add balsamic vinegar and salt, stir to mix. Let it cook for another 3-4 minutes. Set the pan aside.
After adding the balsamic vinegar, put the 12" pan onto the stove, add oil, and turn the heat to high. When the pan is hot, add the roast beef to the pan. When both sides of the beef turn slightly brown, remove the pan from the heat.
When both the veggie and beef are on the stove, cut the bread in half, put the cheese on half of the bread. Place the bread onto the baking tray. Toast for about 2-3 minutes. Use a hand to press the bread. If it is turning crunchy, take the tray out of the oven.
Assemble the sandwich