Pre-heat the oven to 375F (190C) and spray a 9 x 9 (22 x 22cm) casserole with cooking spray
In a large mixing bowl, add the eggs, half and half, salt, and pepper. Whisk thoroughly. Mix in the cheese.
In a large skillet over medium heat, add oil and garlic. Sauté for 1 minute. Add in the mushrooms and sauté for 1 minute more. Finally, add in the spinach and mix in with the mushrooms. Continue to sauté until the spinach is wilted. Remove from the heat.
Add the spinach and mushrooms to the bowl with the eggs. Mix to combine. Pour into the greased casserole and lay the bacon pieces on top in a single layer.
Bake in the pre-heated oven for 30 minutes or until the casserole is set in the middle.
Serve hot, or wrap portions in foil or plastic wrap and store in an airtight container in the fridge up to 1 week.