Season the chicken pieces with salt, pepper, and oregano. Heat a large Dutch oven over medium high heat, add some oil. Working in batches, brown the chicken on both sides. Remove to a platter as they are browned.
Add more oil to the Dutch oven if needed, then add the green pepper, onion, and garlic. Saute until the onion is translucent, about 8 minutes.
Add the rice, and stir to mix with the green pepper, onion, and garlic. Stir the rice to toast it, about 5 minutes. Then add the bay leaf and saffron threads.
Pour the chicken broth and diced tomatoes into the Dutch oven and stir to combine.
Return the chicken pieces to the Dutch oven, laying them on top of the rice and vegetables.
Cover and bake for 1 hour and 20 minutes.
Remove from the oven, sprinkle the green olives and pimentos over the top. Serve immediately with buttered green peas.
Notes
If you don't have a large Dutch oven, you can brown the chicken, vegetables, and rice in a large skillet and transfer everything to a large baking dish.