Boil pasta according to package directions. In a large bowl, combine drained, cooked pasta, broccoli, onion, red pepper, mushrooms, and peas. Toss to mix well. Pour Italian salad dressing over the pasta salad and mix well. Refrigerate for at least 2 hours before serving.
Italian Salad Dressing
Combine all ingredients in a medium-sized bowl and whisk until thoroughly combined and the dressing is smooth. Refrigerate any leftover salad dressing.