Grate zucchini and onion into a medium bowl, and drain off excess juices. Stir in the oregano and salt and pepper to taste.
Heat a frying pan over medium high heat and melt butter in the pan. When butter has coated the pan, arrange the zucchini in a flat layer over the bottom of the pan. Fry until golden brown on both sides, about 5 minutes per side. Serve warm.