Prepare the fiddleheads by washing them, peeling off any brown papery skin (most won't have that but some might), and slicing off any brown ends. Fill a large bowl with cold water and add the fiddleheads, swishing them around with your hands to remove any dirt. Discard the water and repeat this process another time.
Bring a saucepan of water to a boil. Add the fiddleheads and cook them for 10-15 minutes. Drain and rinse them in a colander.
In a large skillet, heat the olive oil and 1 tablespoon of the butter over medium heat. Add the garlic and the fiddleheads, and cook for a few minutes. Stir in the other tablespoon of butter, lemon juice, and lemon zest. Cook for another few minutes, and serve warm. Enjoy!