For the pilaf: Bring the water and lentils to a boil in a medium saucepan. Adjust the heat to a simmer, cover and cook for 15 minutes. Meanwhile, fry the onions in the olive oil over medium heat until well browned, about 12 minutes. Season with salt and pepper, to taste. Add the onions, bulgur, 1 1/2 teaspoons salt to the pan with the lentils, bring to a full simmer, and then cook covered for 5 minutes. Remove from the heat and let stand for an additional 15 minutes. Transfer pilaf to a platter and top with the tomato and herbs. Serve drizzled with the Tahini-herb sauce.
Puree all the ingredients in a blender or a mini food processor to make a pale green sauce. (This can be made ahead and kept in the refrigerator for up to 4 days.) Note: This sauce is also great used as a dip, spread, or salad dressing.