Cook pasta according to package instructions and drain when finished.
In a large high-lipped skillet, cook onions and ground beef until browned. Add in the Ragu sauce and let simmer for 15 minutes.
Preheat the oven to 350 degrees F and spoon a little sauce into the bottom of a 9x13-inch pan and spread it around. Layer as follows: 1/2 of the ziti, 1/2 ricotta cheese, 1/2 sauce mixture, remaining ziti, remaining ricotta cheese, remaining sauce mixture, top with mozzarella and basil.