Bring a pot of water to a boil. Add string beans, and cook for 5 minutes. Drain the beans in a colander and immediately pour cold water over them, which will help set the green color and prevent them from cooking further.
Toss the beans with the olive oil.
Meanwhile, heat a large pan over medium-low heat. Add the green beans and ranch dressing to the pan and saute the mixture for approximately 3-5 minutes, until crisp tender.
Toss the crumbled bacon into the dish right before you serve it, so that the bacon stays crisp.