Toast the bread in a toaster or in the oven until lightly golden brown.
Heat the olive oil in a large skillet over medium-high heat. Add the garlic and mushrooms and cook for 3 minutes, stirring occasionally. Add the salt and pepper.
Add the spinach to the skillet and cook for an additional 2 minutes, stirring occasionally, until the spinach is wilted.
Top each slice of toast with an equal amount of mushroom mixture. Sprinkle with Parmesan cheese and serve.