Rinse and remove any stems from the green beans. You don't have to remove the tips, just the stems.
Heat enough water to fully submerge the beans in a large pot over high heat. Once the water begins to boil, add the beans and cook for 3-5 minutes until they are bright green. Drain the beans from the water.
In a glass or small bowl, stir together the soy sauce and miso paste.
In a large skillet or wok, heat the oil over medium/high heat. Cook the beans for about 3 minutes, until some of them begin to blister. Add the garlic, and cook another 2 minutes. Pour the soy and miso mixture over all the beans, and cook for an additional minute.
Pretty quick cooking time, huh? You can cook these a bit longer depending on what type of texture you prefer. These are pretty cooked through, but still taste fresh. I'm not a major fan of mushy green beans, so this is how I prefer it, but you do your thing. Remove to a plate and top with sesame seeds, if using. Serve warm.