In a large pot, bring the water to a boil. While you're waiting for the water to come to a boil, you can trim the ends off your green beans. Once the water has come to a boil, add the salt and green beans, reduce heat and gently boil until very tender, about 10 minutes, then drain in a colander.
Place the sliced scallions and garlic into a large bowl, along with a tbsp of butter. Place the drained green beans into the bowl. Add the black pepper and toss until the butter has melted and coated the green beans.
Notes
If you prefer your green beans to still be a bit crisp, simply cook them until just tender, about 4-6 minutes.