Heat the oil in a large, heavy bottomed sauté pan over medium-high heat. Add the rice and cook, stirring constantly, until it's a light golden brown. About 3 minutes.
Reduce the heat to medium. Add in the onion, potato, garlic, tomato paste, taco seasoning, cumin, and salt. Cook, stirring frequently, for about two minutes. The onion should be slightly softened, and the tomato paste evenly incorporated.
Slowly pour in the tomato sauce and chicken stock. Gently stir until it's evenly combined. Stir in the corn kernels.
Increase the heat back up to medium-high, and bring the mixture to a boil. Reduce the heat to low, cover the pan, and let it simmer for 25 minutes.
Turn off the heat and let it sit, uncovered, for 5 minutes. Fluff with a fork and top with cilantro if using.
