Cut the tops off each tomato and scoop out a small amount of the insides. Discard tops and insides.
Heat olive oil in a skillet over medium heat; cook and stir zucchini, green bell pepper, garlic, and salt until tender, about 10 minutes. Add ground turkey; cook and stir until turkey is browned and crumbly, 5 to 7 minutes. Stir quinoa and 1/2 of the tomato sauce into the ground turkey mixture.
Arrange tomatoes in a baking dish. Fill each tomato with turkey-quinoa mixture. Pour remaining tomato sauce over each stuffed tomato. Pour a 1/2 inch of water into the bottom of the baking dish.
Bake in the preheated oven until tomatoes are tender, about 15 minutes.