Add oil, rice, serrano and onion to skillet. Heat to medium heat. After a few minutes, the rice will begin to toast. Stir as needed until the rice, onions and serrano become aromatic and begin to toast and brown lightly.
While the rice toast, on another burner, add the water(or broth) and bouillon. Heat on medium and stir just to dissolve the bouillon. Do not let it boil.
To the blender, add the tomatoes, garlic, oregano and a pinch of salt. Blend until smooth. You may need to use a spatula to scrape the ingredients down so they will blend smoothly. Do not add any water to the tomatoes when blending. Once the rice is toasted, add the blended tomato sauce from blender. Gently stir to combine and cook for 5 minutes or until the sauce reduces and becomes thick.
Add the warm broth to the skillet. It will come to a boil quickly. Stir gently, taste for salt and season with some fresh cracked pepper. Add the cilantro, reduce heat, cover pot and then cover with the lid tightly. Do not disturb the rice as it cooks. Do not remove the lid. Let it cook for 10 minutes. If you are adding the frozen peas and carrots, add them now. Set timer for another 5 minutes. After 5 minutes, check the rice to see if liquid has evaporated. If it has evaporated, remove from heat and let stand for 10 minutes. Remember that all stove tops and cookware will vary on the time the rice is done.
Remove the large pieces of onion and cilantro. Fluff the rice with a fork stirring from the outer edges in to combine everything. Keep covered until ready to serve.