Add 1/4 cup of olive oil to a small pan over low-medium heat.  Once it is hot, add the sliced onion, sliced red pepper, and 1/2 tsp of red pepper flakes.  Let the oil slowly soften the vegetables. 

While the veggies are cooking, cut open your sub roll and scoop out the bread from each side of the roll.  

Spread mayo and spicy mustard (if using) on sides of roll. 

Place sliced cheese on each side. 

On one side, place half of the meat, lettuce, and tomato slices.  On the other side, place the rest of the meat and top with the cooked onions and peppers.  

Using a spoon, drizzle some of the flavored oil over each side of the sandwich.  

Top with a small drizzle of red wine vinegar, a sprinkle of Italian seasoning, and a small pinch of red pepper flakes (if you like the heat).  

Leaving the sandwich open, toast for 2-3 minutes.  

Close sandwich and enjoy!