PLACE pasta in large bowl. Chop 1 pepper. Add to pasta with 6 Tbsp. dressing; mix lightly.
COOK mushrooms in remaining dressing in skillet on medium-high heat 4 to 5 min. or until tender, stirring frequently.
ARRANGE remaining peppers and all remaining ingredients except oregano in clusters in large shallow serving bowl. Sprinkle with oregano. Refrigerate 1 hour. Toss before serving.