Place the lentils and water in a small saucepan over high heat. Bring to a boil, stir, then reduce the heat to medium-low. Cook, uncovered, stirring from time to time, 15 to 20 minutes, until the water has mostly absorbed and the lentils are tender and broken down.

Meanwhile, heat the olive oil in a large pot over medium-high heat until it shimmers. Add the onion and cook, stirring a few times, about 4 minutes, until the onion has softened and its color starts to fade. Add the tomato and cook, stirring often, for 2 minutes. Stir in the tomato paste and garlic and continue to cook, stirring often, 1 to 2 minutes more, until the juices have mostly evaporated. Stir in the cumin, coriander, pepper and crushed red pepper flakes, if using, to incorporate.

Add the cooked lentils and the salt, stir, and reduce the heat to low. Continue to cook and stir occasionally for about 5 minutes, or just until the mixture starts to bubble. (It may spit and sputter, so be careful.)

Meanwhile, if making the optional oil topping, heat 2 tablespoons of olive oil in a small skillet over medium heat. Add the garlic and cilantro and cook, stirring occasionally, 3 to 5 minutes, until the garlic is golden and the cilantro is a little crispy on the edges.

Remove the stew from the heat and stir in the chopped parsley, then stir or swirl the oil-garlic-cilantro mixture into the stew. Serve right away.