1. Put lentils in a pan, sprinkle with 1/2 tsp. salt. Cover with 1 inch cold water. Bring to a boil. Reduce heat to medium-low; simmer until lentils are just tender, 15 to 20 minutes. Drain. Transfer to a bowl. Let cool.
2. Add yogurt, 2 Tbsp. olive oil, cilantro, garlic, cumin and cayenne. Gently stir and season with salt. Divide greens among 4 plates; mound lentils in center. Place tomatoes (and cucumbers, if desired) on the side and drizzle remaining olive oil over all. Serve immediately.