In a 6- to 8-inch frying pan over medium-high heat, stir or shake white sesame seed until golden, 4 to 5 minutes (don't toast black sesame seed). Pour into a small bowl.
To sesame seed, add beets, yogurt, onion, sumac, and thyme; mix.
Arrange a lettuce leaf on each plate and mound beet salad equally onto leaves. Add salt and pepper to taste.