Heat a large non-stick pan over medium heat. Spray with cooking spray and add 1 teaspoon olive oil.
Add the onion to the pan, cook until soft (about 4 minutes). Add the mushrooms and tomatoes. Cook until the tomatoes start to break down.Add salt and pepper to taste.
Add the swiss chard, cover and cook about 4 minutes or until the swiss chard is wilted. Toss well and serve!
