Add water, onion, garlic, tomatoes, tomato paste, and chicken bouillon to a blender. Blend until completely smooth.
Pour the blended mixture through a fine mesh strainer into a bowl, keeping only the liquid. (You can save the thicker leftover pulp as a fresh, salsa-like topping for your meal.)
Rinse the rice in a strainer under cold water for about 1–2 minutes, until the water runs clearer. Let excess water drain well.
Heat a large, wide pan over medium-high heat. Add oil, then add the rice. Cook for about 2–3 minutes, stirring frequently, until the rice starts to turn slightly golden and smells lightly nutty. (This step builds flavor—don’t skip it!)
Carefully pour the tomato mixture into the pan with the rice.
Add salt and pepper. Stir to combine.
Bring to a light boil, then reduce heat to low, cover, and simmer for 25–30 minutes, or until the liquid is absorbed and the rice is tender.
Fluff with a fork, garnish with fresh cilantro, and serve with your favorite Mexican dishes.