Preheat your oven to 350 degrees.
Cut the top 1/4 off of your loaf of bread and set it aside (save the top to make breadcrumbs).
In a large saute pan, heat oil, add garlic and saute 1 minute or until fragrant.
Add in the spinach and saute until wilted. Season with red pepper flakes, salt & pepper. Set aside and cover it with a lid.
Saute your mushrooms and peppers in a bit of melted butter. Season with salt & pepper. Saute until tender about 5-6 minutes (longer if your mushrooms are large).
Place your spinach atop the bread, nestle on the sauteed peppers and mushrooms.
Place it in the oven on a baking sheet for 4-5 minutes. Just until the bread gets warmed.
Sprinkle with Feta cheese, slice and serve.