Preheat the oven to 210 °C.
Cut the bread into slices of about 2 cm.
If you are using frozen spinach, defrost it in the microwave for a few minutes at 300 Watt or take it out for a few hours to defrost in the open air.
Sauté the spinach in a pan with a little olive oil for about 5 minutes. Do not overcook the spinach as it will continue to cook in the oven later.
Add a chopped clove of garlic. Season with salt and pepper. Set aside for later.
Sauté the mushrooms in a pan for 5 minutes until lightly browned. Don't overcook them either as they will also continue to cook in the oven. Season with salt and pepper.
Cut the cheese into two to three thin slices per slice.
Assemble the slices.
Place a portion of spinach on each slice of bread. Then place a few mushrooms on top. Finally, cover with cheese. Season with salt and pepper.
Place the toasts on a baking sheet covered with baking paper. Bake for 15 minutes.