Bring a large pot of lightly salted water to a boil, add the pasta and cook until tender, about 8 minutes Drain and rinse under cold water to cool. Meanwhile, in a large deep skillet over medium-high heat; cook the bacon until browned and crisp and remove from the pan and drain on paper towels In a large bowl, stir together the dressing, onion, and tomatoes and then mix in the cooled pasta and then refrigerate for several hours or overnight and crumble bacon over the top just before serving