Heat 2 tablespoons of olive oil in pan at medium heat and add sliced onion. Stir the onion until it is coated with oil. Add salt.
Stir the onions every five minutes or so. Cooking will take about 35-40 minutes.
Add a small amount of vinegar to deglaze the pan and cook a couple more minutes.
Spread roasted red pepper hummus on a tortilla, add sliced tomato and caramelized onion.
Heat olive oil in a pan. Add tortillas with filling. Cook until golden brown. Then, flip and cook other side.
Notes
I recommend making this roasted red pepper hummus quesadilla right before you eat it. The individual components (caramelized onions, roasted red pepper hummus) will last up to 5 days in airtight containers in the fridge.