Bring a pot of salted water to a boil over high heat. Mince the garlic and half the onion, and coarsley chop the basil leaves and scallions.

Heat 1 tablespoon of oil in a pan over medium-high heat. When the oil is hot, add the onion and the garlic and sauté until just brown, about 5 minutes. Transfer to a bowl and reserve.

When the onion mixture is cool, add the panko, chicken and mustard to the bowl. Season with salt and pepper and mix well. With wet hands, form the mixture into meatballs the size of Ping-Pong balls.

Heat the remaining oil in the pan on high and swirl to coat the bottom. When the oil is hot, add the meatballs. Sauté the meatballs on all sides until brown, 4 to 5 minutes.

Cook the pasta in the salted boiling water until al dente, about 11 minutes. In the meantime, add the scallions, tomato sauce and basil to the pan with the meatballs and mix.

Reduce the heat under the sauce and meatballs to medium-los and simmer to blend the flavors, about 8 minutes covered. When ready, drain the pasta and add to the pan with the sauce, tossing together well.