Boil a large pot of salted water. Add the green beans and cook until tender crisp, 1 to 2 minutes. Use a slotted spoon or spider to remove to a bowl of ice water. Drain well, pat dry and place the beans in a large bowl. Add tomatoes and red onions.
Toast the almonds in a small skillet for 2 to 3 minutes. Remove to a plate to cool.
In a small bowl, whisk together the olive oil, red wine vinegar, basil, garlic and salt and pepper to taste. Pour the dressing over the green beans and sprinkle with the toasted almonds. Let marinate in the refrigerator for 1 hour. Just before serving toss in feta cheese.