Heat oil in a large (5- to 7-qt.) Dutch oven or other heavy pot over medium heat. Add white and pale-green parts of green onions; cook, stirring often, until just softened, about 2 minutes. Mix in bell pepper; cook, stirring often, 2 minutes. Add rice; stir to coat in oil. Stir constantly, until toasted, about 1 minute. Add water, salt, and black pepper; bring to a boil over medium-high. Reduce heat to medium-low; cover and simmer, 15 minutes.