Heat oil in medium, heavy-bottomed pot over medium heat; add onion, bell pepper, garlic, capers (if using), olives and oregano. Cook, stirring occasionally, until vegetables begin to soften and become fragrant, about 3 minutes. Stir in tomato sauce.
Stir kidney beans into pot until well combined. Add 3 cups water and bring to boil; season with salt.
Stir in rice until well incorporated; reduce heat to medium. Simmer until water has evaporated, about 5-7 minutes. Stir rice once from bottom to top, scraping bottom of pot with spoon. Reduce heat to low; simmer, covered, until rice is tender, about 15-20 minutes. Add cilantro to pot; fluff rice with fork. Serve.