Bring a medium pot of water to a boil and add sliced potatoes. Cook ~ 6-8 minutes or until firm but done (remember you are going to bake it again so you want al dente). Drain and set aside.
Mix the eggs and add a little salt and pepper.
In greased pan, layer the potatoes, spinach, tomatoes, olives, capers, and feta cheese.
Add eggs on top of everything and gently push any ingredients sticking up into the eggs (it's ok if stuff is still sticking out, it will just get drier - see picture).
Place baking dish on a sheet pan in case your frittata fluffs up and spills over in your stove.
Bake at 375F for ~ 30 minutes or until set. Broil in the last couple minutes (watching carefully that it don't burn) if you want the top a golden brown.
Let cool and serve. Happy eating! Beckie
Notes
Don't like potatoes? Leave 'em out or substitute a small sweet potato.
Like feta cheese? Add a little more. All the amounts can be substituted a little to your preference just depending on what your baking dish can hold.
Don't have or like feta? Cool - substitute the cheese of your choice.