This fiddlehead frittata is great served hot or cold. We recommend using a cast iron skillet, but any oven-safe, high-walled saucepan will work.
Bring a small pot of water to a boil. Clean fiddleheads, removing brown fuzz and trim the ends. Then cook in boiled water for about 10 minutes.
Meanwhile, sauté diced onion, minced garlic and sliced mushrooms in olive oil, until tender. Add cooked fiddleheads, salt and pepper, cook a few more minutes until everything is tender but not mushy. Lower heat and add in minced oregano.
In another bowl, whisk together the eggs with a pinch of salt and cheese if using. Add egg mixture to the vegetables, tilting pan slightly to ensure even distribution. Cook over low-med heat until eggs begin to set, around 10 minutes.Finish cooking under broiler for about 3 minutes.