Put the favas, 1/2 cup liquid, the lemon juice, and a sprinkling of salt and pepper in a large, deep skillet over medium heat. As the beans begin to heat, roughly mash and stir them with a potato masher or fork. If they begin to stick to the skillet, add more liquid--a little at a time--to loosen them to the consistency you like. Transfer the beans to a shallow serving bowl or platter. Wipe out the pan, add the oil, and return it to medium heat. When the oil is hot, add the onion, garlic and cook, stirring occasionally, until they begin to soften, 3 to 5 minutes. Add the tomatoes, feta, and a sprinkle of salt and pepper and cook, stirring, only until the tomatoes are warmed through and the cheese softens, just another minute or 2. Spoon the tomato and feta mixture over the mashed favas, making sure to drizzle the pan juices over everything. Garnish with the herb and serve with lemon wedges.