If you pile a bunch of washed and stemmed greens like chard or spinach or kale in a shallow skillet with a few tablespoons of water, cover them and set over high heat, they’ll steam just fine without a proper steamer; most of the water evaporates by the time they’ve become tender, so they’ll be no loss in vitamins. Then, you can add some olive oil or butter to the bottom of the pan to saute the greens.
The problem is that the bulky greens defy the lid, lifting it up, making it impossible to have the seal necessary for steaming. I recommend keeping a rock handy for weighting down the lid.I found the rock, above, on a beach in France when I was looking for a suitable stone to be a make-shift pestle to pound thyme, rosemary and olive oil in a big mortar at the house I was staying in. It is also good for crushing cloves of garlic right on the counter, and cracking spices like peppercorns and coriander seed. I seem to find new uses for it every week.
Rocks foraged on the beach or outdoors have endless uses at home. This smaller rock keeps the freezer door of my office fridge closed: