Wash your hands well with soap and warm water for at least 20 seconds.
Drain mushrooms.
Heat large skillet over medium heat. Add oil.
Add vegetables and mushrooms and cook until water evaporates and vegetables are tender. Add spinach and stir to break apart. Cook about 5-10 more minutes.
Fill pie crust with vegetable mixture and top with shredded cheese.
In a mixing bowl, whisk eggs together and add milk, lemon juice, salt, pepper, and garlic. Whisk to combine. Pour over cheese and vegetable mixture in pie crust.
Place on baking sheet and bake 30-35 minutes, until the middle is set, and a knife inserted in the middle comes out clean. Let cool 5 minutes before cutting. Cut into 8 wedges and serve.