01 -
Get your oven ready at 400°F. Twist off the stems from the mushroom caps but be gentle to avoid breaking the caps. Stir together 1/4 cup olive oil, balsamic vinegar, a pinch of garlic powder, and sage. Place the mushrooms in this flavorful mix to soak it all up while you get the other components going.
02 -
Chop up the spinach roughly, removing thicker stems if you spot any. Mince your garlic into small pieces and set it aside for later.
03 -
Place a pan on medium heat and pour in 3 tablespoons olive oil. Toss in the minced garlic and let it sizzle for a few minutes until fragrant and golden. Add the chopped spinach and cook gently for about 4 minutes until it softens, stirring now and then. Add salt and pepper to taste.
04 -
Put the marinated mushroom caps onto a baking sheet with the gilled side facing down. Roast for 10 minutes.
05 -
Flip those mushrooms over and pour off any juices. Fill them with your spinach mixture, then sprinkle feta cheese over the top, roughly 1½ tablespoons each. Put them back in the oven for another 20 minutes or so, until they're bubbling and golden.