Preheat oven to 350°F. Liberally spray six cups of a regular-size muffin tin with Cooking spray.
Line each one of the sprayed cups with one slice of turkey breast, if using.
Divide the 1 ½ cups chopped baby spinach evenly between each cup, pressing down to pack in.
Carefully break an egg into each cup—it’s okay if a little bit spills out of the turkey “bowl.”
In a small bowl, mix together the ½ teaspoon sea salt, ½ teaspoon black pepper, and ¼ teaspoon garlic powder. Sprinkle evenly over the egg cups.
Bake in preheated oven for 10-12 minutes (for a soft yolk), or 12-15 minutes (for a hard yolk). Let cool for 10 minutes in the muffin tin, then use a knife to loosen the sides of the cups and lift them out with a spoon.