Combine the water and measured salt in a medium saucepan and bring to a boil over high heat. Add the bulgur, stir to combine, and remove the pan from the heat. Cover with a tightfitting lid and let sit until the bulgur is tender, about 15 minutes. Drain well through a fine-mesh strainer, pressing out the excess liquid, and place the bulgur in a large bowl. Let cool to room temperature.
Meanwhile, place 2 teaspoons of the oil in a small frying pan, add the pine nuts, season with salt and pepper, and stir to coat. Toast the nuts over medium heat, stirring occasionally, until they’re golden brown and fragrant, about 3 to 5 minutes. Remove the pan from the heat and set aside until cooled.
Add the parsley, mint, scallions, tomatoes, and cooled pine nuts to the cooled bulgur and stir to combine.
Place the lemon juice, remaining 1/2 cup oil, and sumac in a small, nonreactive bowl and whisk until combined. Add the dressing to the bulgur mixture and stir to combine. Taste and season with salt and pepper as needed. Cover and refrigerate for at least 15 minutes or up to 6 hours.
When ready to serve, prepare the lettuce leaves. Discard any tough or bruised outer leaves and cut off and discard the stem end. Separate the leaves and cut each leaf in half crosswise. Wash and dry thoroughly. Line a large serving plate with the lettuce leaves. Drizzle the tabbouleh with olive oil, if desired, and toss to combine. Spoon onto the lettuce leaves and serve.