In a large saucepan cook squash, covered, in enough lightly salted boiling water to cover until tender, about 5 minutes. Drain. Cool vegetables by adding cold water and ice cubes to pan. Drain well.
In a serving bowl combine the drained squash, tomatoes, arugula, and herbs. In a screw-top jar, combine remaining ingredients. Cover; shake well. Add half to salad; toss to coat. Season to taste with additional salt and pepper. Pass remaining dressing. Makes 8 servings.