Wash the greens and dry them by firmly holding the stems and flicking them over the sink.
Discard heavy stems, except with the chard.
Tear or cut the greens into bite-sized pieces.
Cut the heavy center rib and stems with scissors, if needed.
Heat the olive oil in a skillet on medium-high heat.
Add the most substantial greens, garlic, oregano, and optional pepper flakes.
Cook, stirring often, for 1-2 minutes, just until the greens wilt.
Add other greens in batches as described in the Cook’s Tip below.
After you’ve added everything, check your greens for tenderness.
You might need to add a tablespoon or so of water and cover the pan to steam the greens briefly, 1-2 minutes, until everything is tender.
Serve immediately.