Cook the Gnocchi: Boil salted water in a large pot. Add gnocchi and cook until they float (about 2-3 minutes). Drain and toss with olive oil.
Sauté Aromatics: In a skillet over medium heat, add olive oil. Sauté onions until softened (5-7 minutes), then add garlic and optional red pepper flakes. Cook for another minute before adding spinach.
Create Sauce: Stir in heavy cream and chicken broth; simmer for about two minutes. Incorporate feta and half of the Parmesan until melted.
Combine: Add cooked gnocchi to the skillet and toss to coat in the sauce. Stir in butter and sprinkle remaining Parmesan on top.