Caprese Quiche

Preheat the oven to 350 degrees F (175 degrees C). Place pie crust in a pie pan or baking dish.

Heat olive oil in a skillet over medium heat. Cook and stir onion until softened and translucent, about 5 minutes. Reduce heat to medium-low, and continue cooking and stirring until onion is very tender and dark brown, 15 to 20 minutes more.

Spread mozzarella cheese and tomatoes over the bottom of pie crust. Whisk eggs, lemon juice, basil, salt, black pepper, and caramelized onion in a large bowl; pour mixture over cheese and tomatoes.