Place green beans into a large stock pot. Cover with water leaving 2 inches headspace. Add 1 teaspoon salt. Bring to a boil. Once at a boil, lower the heat to medium and simmer for 5-8 minutes or just until crisp tender.
Drain green beans well and set aside.
Meanwhile, in a stand blender add cider vinegar, lemon juice, Dijon, garlic cloves, 1 tsp salt, sugar, black pepper and onion powder. Pulse a few times to combine. With blender on low slowly add vegetable oil through the top until dressing is slightly thickened. Taste and adjust salt to taste. (The Parmesan cheese will add to the saltiness of the dish overall.)
Place warm green beans and red onion in a large bowl and drizzle with dressing. Mix well. Cover and chill until completely cooled.
Once cooled, add tomatoes and Parmesan, toss to combine. Chill until serving.