Rinse rise in a strainer until water runs clear. If able to prep ahead, leave to air dry overnight. Otherwise, set aside.
In a medium sauce pan add water and bouillon or chicken broth and place over medium heat. Bring to simmer or slow boil and turn heat off.
While broth simmers, place large pan over medium heat and add oil and onions. Once oil is hot and onions are fragrant add rice. Cook until rice is slightly golden being careful to not brown too much.
Bring heat down to medium low and add tomato sauce and broth to rice. Add in sazon if using. Carefully stir only to combine everything. Cover with lid and cook for 15 minutes.
After 15 minutes check to see if all water is absorbed. If not, leave on for another 2 minutes and check again. Once all water is absorbed remove from heat and fluff rice with fork.