1. In a small saucepan over medium heat, cook the lentils in 1 cup water, covered, until the water is absorbed and the lentils are soft, about 20 minutes.
2. In a medium saucepan over medium heat, sauté the onion, cumin, turmeric, and garlic powder in the oil until softened, about 5 minutes. Add the lentils and cornmeal and cook, stirring, until thickened, about 2 minutes. Add the tomato sauce, sriracha, and chili flakes and cook for 3 to 4 minutes, or until thickened. Mix in the salt, pepper, and 2 teaspoons of the lemon juice.
3. In a small bowl, combine the remaining 2 teaspoons lemon juice, the lemon zest, and the yogurt.
4. Top the bread with red lentil mash, a dollop of citrus yogurt, and the chopped herbs.