Trim the ends from the green beans and rinse them well.
In a large skillet set over medium heat, add the balsamic vinegar and minced garlic. Heat until the mixture begins to warm and lightly simmer.
Add the green beans to the skillet and toss to coat. Cover and cook for 8–10 minutes, stirring occasionally, until the green beans are tender and infused with the balsamic flavor.
Remove from the heat and transfer the green beans to a serving dish. Sprinkle with chopped walnuts just before serving.