Heat oil in a medium skillet over medium heat. Add onion and bell peppers; cook for 3-5 minutes until fragrant. Add garlic and cook for 1 minute.
Add sausage and cook until browned on both sides, about 5 minutes. Add rice and cook for 2 minutes, stirring constantly.
Add vegetable broth and saffron, if using, and mix well. Test taste and adjust salt and pepper if necessary. Cook uncovered, over medium-high heat, until most of the liquid has evaporated.
When the liquid has evaporated cover, reduce heat to low and cook for 15-20 minutes, or until rice is tender.
Garnish with cilantro, if desired. Serve hot.