In a large skillet, heat 1 tsp of oil over medium-high heat. Add chicken breasts and sear for 1 to 2 minutes per side until golden brown. Transfer to a baking dish.
Heat remaining oil in the skillet. Add zucchini and onions and saute for 3 to 5 minutes until lightly browned. Remove from pan and place on top of the chicken.
In a bowl, mix the tomato sauce and Italian seasoning. Pour over the chicken and vegetables. Sprinkle with mozzarella and Parmesan cheese on top.
Bake in a 350°F oven for 30 minutes or until juices run clear on the chicken when it’s pierced with a fork.