Oil in large skillet on medium-high heat. Add squash; sauté 7 min. or until browned and crisp-tender. Add onions; sauté an additional 2 min.
Broccoli, mushrooms, stock and 3 cups of the dressing (or 1/2 cup of the dressing for trial recipe); stir until well blended. Reduce heat to medium-low; cover. Simmer 3 min. or until vegetables are tender. Uncover.
In 3 cups of the cheese (or 1/2 cup of the cheese for trial recipe) and the remaining 3 cups dressing (or remaining 1/2 cup dressing for trial recipe). Remove from heat. Sprinkle with the remaining 3 cups cheese (or remaining 1/2 cup cheese for trial recipe) just before serving.