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Preheat oven to 400 degrees F (200 degrees C).
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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).
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Heat olive oil in a large skillet over medium heat. Cook onions and vegetables stirring, 5 to 10 minutes. Add onions and any hard vegetables first and cook the longest. Add medium firm vegetables in the middle. Add greens and tender vegetables at the end and cook for just 1 to 2 minutes.
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When all vegetables are soft, remove vegetables from skillet and set aside.
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Whisk eggs, milk, salt, and pepper together in a small bowl.
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Spread 1 cup Colby-Monterey Jack cheese in the bottom of pie crust. Layer vegetable mixture over the cheese. Pour egg mixture into pie shell.
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Place optional tomatoes on top and sprinkle remaining 1/2 cup cheese atop the quiche.
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Bake in preheated oven until a knife inserted near the center comes out clean, 40 to 45 minutes. Cool 5 minutes before serving.