1. Remove any small stones from the black-eyed peas and rinse them well. Place them in a pot and cover with plenty of water. When it boils, add the black-eyed peas. Let them boil for 10 minutes and then drain.
2. Return the black-eyed peas to the pot, add the hot water, and bring to a boil. Lower the heat to medium and boil for 20 minutes. Add the chard to the dish and continue boiling for another 20 - 30 minutes, until the black-eyed peas are almost cooked.
3. Meanwhile, heat the olive oil in a frying pan and sauté the onion for about 3 minutes until softened. Add the olives and continue sautéing for 2 minutes. Add the lemon juice or vinegar, stir, and boil for 1 minute. Pour this mixture over the black-eyed peas (if there is a lot of liquid left, drain some off), add the salt, and boil until the legumes are fully cooked. Add more water if necessary.
