Cook the bacon in a medium nonstick skillet until crisp. Transfer to a paper towel-lined plate to drain; reserve the skillet.
Divide the watercress, cucumbers and radishes among plates.
Season the flour with salt and pepper in a shallow dish. Discard all but 1 tablespoon of the bacon drippings from the skillet, add 1 tablespoon olive oil and heat over medium heat. Working in batches, toss the scallops in the flour and cook until golden on the bottom, about 2 minutes. Turn and cook until golden on the other side, about 2 more minutes (add 1 tablespoon oil, if necessary).
Arrange the scallops over the salads. Add the remaining 2 tablespoons olive oil and the lemon juice to the skillet, then remove from the heat and add 1 to 2 tablespoons water, swirling the pan to release the browned bits. Crumble the bacon and add to the skillet along with the chives, and salt and pepper to taste; swirl to combine, then pour over the salads. Serve with the bread.