Place the green beans in a large stock pot. Cover the green beans with water 2 inches above the beans. Place on the stove over high heat, and bring to a boil.
Once at a boil, lower the heat to medium and simmer for 5 minutes. Strain and set aside.
In a large bowl whisk together the olive oil, vinegar, garlic, dijon, salt, and pepper. Add the warm green beans and onion, toss to coat.
Cover with plastic wrap and place in the fridge to chill for 4 hours or longer if you can.
Before serving add the tomatoes and cheese, toss to combine, and serve immediately.
Type of Oil. If you change the type of oil used in the salad marinade, ensure it doesn't clash with the red wine vinegar. Walnut oil, for example, has a strong nutty flavor that can conflict with vinegar.
Same Day Make Ahead. Since this green bean salad requires time to marinate, it’s a great side salad to make ahead of time. You can prepare it in the morning to enjoy for lunch or allow a longer marinating time and serve it for dinner.
Don't Overcook. The green beans mustn't be overcooked, as this salad is incredibly delicious when the beans are still slightly crunchy. An excellent way to stop the beans from cooking further is to run them under cold water or dump them into a bowl of ice water for a minute or two right after cooking.
Mellow Onions. While I love the thinly sliced red onions in this salad, they tend to have a strong flavor. You can mellow the flavor by soaking the sliced onion in ice water for 15-20 minutes.
Type of Green Beans. I’ve used fresh green beans that have been trimmed as they tend to have the most flavor. If you don’t have access to fresh green beans, use frozen green beans as a second choice, followed by canned green beans. Frozen green beans will require even less cooking time since they have already been blanched.
Type of Oil. I love using olive oil in salad dressings and when cooking. The fragrance of olive blends beautifully with raw vegetables. If you’d like to use a different oil, I suggest one that’s neutral such as corn oil or sunflower oil.
Add Texture. Add some extra crunch with nuts such as pecans, sliced almonds, or seeds.
Add Protein. Turn this marinated green bean salad into a main meal by adding some shredded tuna, grilled chicken, hard-boiled eggs, or crumbled bacon.
Double It. Consider doubling the ingredients if you're serving a crowd - it's that easy!
Vary The Vegetables. Add in other veggies such as asparagus (which should be cooked the same way as the green beans), bell peppers, corn, and garbanzo beans.
More Cheese Please. Mozzarella pearls/balls or crumbled feta cheese are delicious alternatives or additions to the grated parmesan cheese.
Fresh Herbs. Give this green bean salad a further flavor boost by adding in some chopped fresh basil or oregano.