Place 2 pounds fresh green beans in a large pot and add enough water to cover them by 2 inches. Bring to a boil over high heat. Once boiling, reduce the heat to medium and simmer for 5 minutes. Drain and set aside.
In a large mixing bowl, whisk together 1/3 cup olive oil, 3 tablespoons red wine vinegar, 4 cloves garlic, 1 tablespoon Dijon mustard, 2 ½ teaspoons salt, and ¼ teaspoon black pepper until combined. Add the warm green beans and 1 small red onion, and toss to coat.
Cover the bowl with plastic wrap and refrigerate for at least 4 hours. This gives the green beans time to soak up all of the flavors from the vinaigrette.
When you're ready to serve, uncover the bowl. Add 1 pint cherry tomatoes and 1/4 cup grated Parmesan cheese and toss to combine. Serve immediately.
Notes
Marinate for at least 4 hours before serving - overnight gives the best flavor.
Serve cold or let the salad sit at room temperature for 15 to 20 minutes before serving.
Stores in an airtight container in the refrigerator for up to 4 days. Do not freeze.
Mix-in ideas: asparagus, bell peppers, corn, garbanzo beans, sliced almonds, hard-boiled eggs, bacon, fresh basil, or mozzarella pearls.