Warm the olive oil in a medium skillet over medium heat. Add the raw rice, and stir to coat the grains. Add the onion and sauté, stirring constantly, until the rice turns a pale golden brown, about 5 minutes. Lightly coat the bottom and sides of a slow cooker crock with olive oil. Add the browned rice to the crock, along with the broth, tomatoes, garlic, bell peppers, chili powder, cumin, and salt. Stir, cover, and cook on high for 2 1/2 to 3 1/2 hours, checking after 2 hours to see how well the rice is absorbing the liquid. Cook until all the moisture is absorbed and the rice is tender. Garnish with cilantro and serve.