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 cook sausage over medium-high heat until brown, using a wooden spoon to break up meat as it cooks. Drain off fat. Set aside 1/2 cup of the tomatoes; add the remaining tomatoes and the tomato sauce to sausage in skillet. Cook for 6 to 8 minutes or until tomatoes begin to soften.
Divide pierogies among four serving plates; spoon tomato mixture over pierogies. Top with the reserved tomatoes and the watercress.