Bring a large pot of water to a boil. Add 1 teaspoon salt. Cook green beans until tender, 5-10 minutes. While they cook, prepare a large bowl with an ice water bath. Immediately drain the beans into a colander (or scoop them out with a slotted spoon) and place the drained beans in the ice water for a few minutes to stop the cooking. This will keep them bright green and perfectly tender.
Drain the beans and pat them dry. Toss them in a bowl with the tomatoes.
For the dressing, whisk together the olive oil, lemon juice, vinegar, salt, garlic powder, and pepper. Pour the mixture over the green beans and toss to coat. Cover the bowl and chill for at least an hour or up to 3 hours before ready to serve.
Stir in the feta cheese and bacon right before serving. Serve chilled or at room temperature.