Preheat the oven to 350 degrees F.
In a heat-proof bowl, pour the boiling water over the bulgur wheat. Add the lemon juice, 1/4 cup olive oil, and 1 1/2 teaspoons of salt. Stir. Cover the bowl with plastic wrap and allow the bulgur to stand at room temperature for about 1 hour.
Place the chicken breast on a baking sheet and rub it with olive oil. Sprinkle liberally with salt and pepper. Roast for 35 to 40 minutes, until just cooked. Set aside until cool enough to handle.
Remove the chicken meat from the bones and discard the skin. Cut the chicken into medium dice and add to the tabbouleh. Add the scallions, mint, parsley, cucumber, tomatoes, 2 teaspoons salt, and 1 teaspoon pepper. Season, to taste, and serve immediately or cover and refrigerate. The flavors will improve as it sits.