Salt and pepper
Snap ends off green beans. Wash and let dry in colander.
Heat a skillet large enough to hold the beans comfortably (or cook in batches). Add olive oil to glaze the bottom of the pan.
Add green beans to skillet. Be prepared for a lot of noise, as water from the green beans will pop in the oil.
Use long tongs to give the green beans a quick turn in the skillet before covering the pan.
You can also turn the beans by shaking the skillet, but I use cast iron, which is too heavy for this method.
Turn the temperature down to medium low.
When the popping has subsided, take the cover off and turn the beans again. They should have a nice coat of olive oil and be turning bright green
Add a 1/4 cup of water to the pan and cover, leaving the lid very slightly ajar for steam release. If the water doesn't sizzle as soon as you pour it in, raise the heat a bit. This will give an additional steam cook for the beans. The amount of water and time of cooking now depends on the thickness of the beans and how well you like them cooked (though cooking much longer than crisp-tender will result in a duller color).
Remove beans to platter.
Drizzle with olive oil and a spoonful or two of balsamic vinegar, to taste.
Sprinkle with crumbled feta.
Serve hot or make ahead and serve at room temperature.