Preheat oven to 350 degrees F.
Place green beans on a baking sheet and cook in oven for about 20 to 25 minutes, flipping green beans about half way through. Once cooked, take out and set aside.
While the beans cook, mix balsamic vinegar, olive oil, lemon juice, garlic powder, pepper, and salt in a small mixing bowl.
Once green beans are cooled, mix in bowl with tomato halves and red onions. Top with dressing and toss around so all vegetables are coated nicely.
Cover bowl and chill in refrigerator for about 1-2 hours.
When ready to serve, sprinkle with light feta cheese and serve slightly chilled or at room temperature.