Pre-heat the oven to 200C/400F degrees.
Scoop the middle part of the zucchinis out to create space for the filling. Bake the empty zucchini boats for 20 minutes.
Place a pan on medium heat and add the olive oil.
Once the oil is hot, add in the onions and garlic and sauté for 3 minutes.
Add in the tomato sauce and the shredded chicken.
Remove the zucchinis from the oven, once they are done, and stuff them with the filling. Sprinkle the cheese on top and bake for another 5 minutes or until the cheese has melted.