Heat the oil in a large skillet over medium heat. Add the green beans and cook, tossing, until crisp-tender, 4 to 6 minutes. Add the garlic and cook until fragrant, 30 seconds; transfer to a medium bowl and let cool slightly.
Add the tomatoes, shallot, and vinegar to the bowl and toss to combine. Season with ½ teaspoon salt and ¼ teaspoon pepper.