Wash, spin dry Swiss chard, removing tough stems. Peel the potato, grate and set in cold water for 5 minutes, drain and pat dry. Chop the onion and garlic. Zest the lemon
In a medium size skillet or cast iron pan, heat 2 tablespoons of the oil. Add the chopped Swiss chard, onion and garlic. Cook, stirring frequently until the onion is translucent, about 3-4 minutes. Remove to a large mixing bowl and cool for about 5 minutes
Add the grated potatoes, flour, salt and pepper, lemon zest and eggs to the mixing bowl and combine until all ingredients are mixed well
Wipe out the skillet you used to cook the chard and onions and heat it with 2-3 tablespoons olive oil over medium heat
While the skillet is heating, shape the patties into golf ball sizes with your hands, adding them to the heated skillet as you shape them. Flatten them to about ½-inch. Don't crowd the pan, you may need to cook them in two batches. Cook them until they are browned, about 5-6 minutes each side
Serve with crumbled Feta or a dollop of mayonnaise