Preheat oven to 350°F. Toss bread with oil and spread on a baking sheet. Bake, turning once, until golden brown, 15 to 20 minutes.
Cut 1 tomato in half. Working over a large bowl, shred both halves using the large holes on a box grater. Discard the skin. Add mayonnaise, chives (or scallion greens), vinegar, garlic powder and pepper; whisk to combine.
Chop the remaining 3 tomatoes. Add the tomatoes, romaine and croutons to the bowl with the dressing; toss to coat. Sprinkle with bacon.