Preheat your oven to 350°F (175°C). Grease a 9-inch pie dish with olive oil or cooking spray and set it aside.

In a large mixing bowl, crack the eggs and whisk them together until well beaten.

Stir in the milk, shredded cheese, salt, and black pepper into the egg mixture until everything is evenly combined.

Heat a tablespoon of olive oil in a skillet over medium heat. Add the sliced mushrooms and cook them for about 5 minutes until they're softened and any excess moisture has evaporated.

Add the diced tomatoes and cooked and crumbled bacon to the skillet with the mushrooms, and stir everything together. Let it cook for another minute to allow the flavors to meld.

Transfer the mushroom, tomato, and bacon mixture to the prepared pie dish, spreading it out evenly.

Pour the egg mixture over the top of the mushroom, tomato, and bacon mixture in the pie dish, making sure it's evenly distributed.

Place the pie dish in the preheated oven and bake the quiche for 30-35 minutes, or until the top is set and lightly golden brown.

Once the quiche is done baking, remove it from the oven and let it cool for a few minutes before slicing and serving.

Garnish the quiche with chopped fresh herbs like parsley or chives if desired, then serve and enjoy your delicious Crustless Quiche with Tomato, Mushroom, and Bacon!