Wash, core and seed the bell pepper. Cut the pepper lengthwise into ½ inch slices.
In a large skillet, heat the olive oil over medium heat. When the oil is very hot, add the sliced peppers and onions. After 4 minutes add the mushrooms. Sautee for another 4 minutes until the peppers are tender but still firm.
Stir in the balsamic vinegar, pepper, and salt.
Cook for an additional minute, sautéing to coat the peppers with the vinegar.
Transfer the peppers, mushrooms and sauce to a dish and serve hot.
