In a medium heavy saucepan, heat the olive oil over medium-high heat. Add the onions, bell peppers, and 1/2 teaspoon of salt and cook, stirring occasionally, until the vegetables have softened, 4 to 6 minutes. Add the garlic and cook for 1 minute longer. Add the rice and oregano and cook, stirring, until the rice turns opaque, about 2 minutes. Add the stock, 1/2 teaspoon salt, the saffron and the drained beans. Bring to a boil, stir, then cover the pot and reduce the heat to low. Cook undisturbed for 20 minutes, then remove the pan from the heat. Let sit, covered, for 5 to 10 minutes. Fluff the rice with a fork and garnish with the cilantro. Serve immediately.