Slice onions in half, then into half-moons.
Melt the oil in a large skillet over medium high heat. Add the onion and salt, stir well to coat, then lower the heat to medium-low. Cook for 20-30 minutes, stirring occasionally.
Once the onions have caramelized to your liking, add the Swiss chard and stir well. Remove from heat and let the warmth of the onions wilt the greens. Add the lemon juice, and season to taste. Say thank you and enjoy, store any leftovers in the fridge for up to 6 days.