Step 1: Wash the swiss chard thoroughly in cold water. Separate the stems from the leaves by slicing along the center rib.
Step 2: Finely dice the stems into 1/4-inch pieces. Roughly chop the leaves into 2-inch wide ribbons and set aside in separate piles.
Step 3: Heat the olive oil in a large skillet over medium heat. Add the diced stems and cook for 3-4 minutes until they begin to soften.
Step 4: Add the sliced garlic and red pepper flakes to the skillet. Sauté for 1 minute until the garlic is fragrant but not browned.
Step 5: Add the chard leaves to the pan in batches, tossing with tongs to coat in the garlic oil. The leaves will wilt down quickly.
Step 6: Once all leaves are wilted (about 3-5 minutes), season with salt and pepper. Remove from heat.
Step 7: Squeeze fresh lemon juice over the greens and sprinkle with parmesan cheese if using. Serve immediately while hot.