Preheat oven to 400 degrees F (200 degrees C).
Bake pie crust in preheated oven until firm, about 8 minutes. Remove crust from oven and set aside. Reduce oven heat to 350 degrees F (175 degrees C).
Heat olive oil in a large skillet over medium heat. Cook and stir onion, green bell pepper, mushrooms, and zucchini in hot oil until soft, 5 to 7 minutes. Remove vegetables from skillet and set aside.
Sprinkle tomato slices with flour and basil; cook in the skillet for 1 minute per side.
Whisk eggs, milk, salt, and pepper together in a small bowl.
Spread 1 cup Colby-Monterey Jack cheese in the bottom of pie crust. Layer vegetable mixture over the cheese and top with the tomatoes. Pour egg mixture into pie shell. Sprinkle remaining 1/2 cup cheese atop the quiche.
Bake in preheated oven until a knife inserted near the center comes out clean, 40 to 45 minutes. Cool 5 minutes before serving.
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