Beef with mushroom

1 (4 lb) top sirloin roast, fat trimmed to 1/4-inch thickness salt and pepper 1 tablespoon vegetable oil 8 ounces white mushrooms , chopped 2 onions , minced[...]

2 teaspoons olive oil 1 red onion , chopped 1 zucchini , shredded 3 carrots , shredded 1 yellow bell pepper , chopped 1 celery , chopped 8 mushrooms , chopped[...]