Start the lentils: Put a medium saucepan on the stove. Add the lentils, 4 cups water, and 1 teaspoon of the salt, then bring the pot to a boil over high heat.

Lower the heat to medium-low so the water bubbles gently. Cook the lentils for 10 to 12 minutes, until they are starting to soften but still a little firm in the center.

Brown the onions: While the lentils cook, set a large skillet over medium heat and add the olive oil.

Add the sliced onions to the skillet. Sprinkle on 1/2 teaspoon of the salt and cook, stirring every 2 to 3 minutes, until the onions soften and turn light gold, about 12 minutes.

Lower the heat under the skillet to medium-low. Keep cooking the onions, stirring often, until they are deep brown and very soft, 8 to 10 minutes more. If the pan starts to look dry, add 1 tablespoon of water so the onions do not scorch.

Build the lentil rice: While the onions finish, rinse the rice in a fine-mesh strainer under cool water until the water runs mostly clear.

Drain the lentils in a colander. Put the drained lentils back into the same saucepan.

Add the rinsed rice, cumin, 1 3/4 cups water, and half of the browned onions to the saucepan with the lentils. Stir once and bring the liquid to a boil over medium-high heat.

When the liquid reaches a boil, cover the saucepan with a tight lid and turn the heat to low. Cook for 15 minutes, until the rice is tender and the water is absorbed.

Turn off the heat and let the covered saucepan sit for 10 minutes so the rice can finish steaming and the grains can settle.

Make the cucumber yogurt: While the lentil rice rests, put the grated cucumber in a clean kitchen towel or a few layers of paper towels. Squeeze out most of the extra water, then transfer the cucumber to a medium bowl.

Add the Greek yogurt, 1 tablespoon lemon juice, 1 teaspoon lemon zest, half of the parsley, the remaining 1/4 teaspoon salt, and the black pepper to the bowl with the cucumber. Stir until smooth, then taste and add a little more salt or pepper if needed.