Defrost and squeeze spinach dry to remove excess moisture.

Slice the onion and mushrooms.

Mince the garlic clove.

Heat oil in a skillet over medium heat.

Saute the onion, garlic, and mushrooms in the oil for about 5 minutes, until softened.

Add the spinach, lemon juice, and ground black pepper to the skillet.

Cook over low heat for approximately 3 minutes, stirring occasionally.

Chop the cooked turkey into bite-sized pieces.

In a bowl, whisk the eggs until well beaten.

Add the chopped turkey and beaten eggs to the spinach mixture in the skillet.

Grease a 9-inch round baking dish with cooking spray or butter.

Pour the frittata mixture into the prepared baking dish.

Bake in a preheated oven at 350°F (175°C) for 25 to 30 minutes, or until the eggs are set and the frittata is golden brown.

Remove from oven and let cool slightly before cutting into wedges.

Serve warm.