Bring water to a boil in a medium-sized sauce pan. Add lentils and cook for about 12-15 minutes, until lentils are soft. Stir in1/4 teaspoon salt until dissolved. Then drain lentils thoroughly, and add to a food processor with the tahini, olive oil and garlic. Blend for 20 seconds, then add lemon juice, turmeric, cumin and remaining 1/2 teaspoon salt. Blend for about 45 seconds, until mixture is completely smooth. Taste and adjust salt or lemon juice as needed.