In a large skillet over medium heat, warm the oil and add the garlic. Saute for about 30 seconds and then add the onions and stir to coat with oil and garlic. Continue cooking for a couple minutes, until it starts to become fragrant. Add the mushrooms and stir to combine. Add the salt and red pepper and toss to coat well. Cook for about 4-5 minutes until the mushrooms are tender.
While the mushrooms are cooking, shake any excess water off the Swiss chard and then remove the stems. Slice the stems very thinly and then add them to the skillet. Stir to combine. Slice the remaining leaves into ribbons and then add to the skillet with the rest of the vegetables. Toss well to coat with oil and seasonings. Saute for another 2-3 minutes until the greens are just barely wilted. Top with grilled chicken if desired and Enjoy!