In a Dutch oven cook pierogies in 4 cups lightly salted boiling water according to package directions. Drain; cover to keep warm.
Meanwhile, in a 12-inch skillet brown sausage. Drain fat. Reserve 1/2 cup of the tomatoes; add remaining tomatoes and tomato sauce to skillet. Cook, uncovered, for 6 to 8 minutes or until tomatoes begin to soften.
Divide pierogies among plates; spoon on sauce. Top with reserved tomatoes and watercress.