In a large kettle using the oil over medium-high heat cook the onion, peppers, and celery until tender. Add the rice and continue cooking until rice becomes translucent around the edges. Stir in the tomato paste and garlic; cook until fragrant.
Stir in the tomatoes and chicken broth, and then season with the salt, and cayenne pepper. Bring mixture to a boil, reduce heat to simmer, cover and continue cooking until rice is tender and liquid is absorbed; about 20 minutes.
Add extra broth or water to the rice mixture if it starts to become too dry before the rice is done
Fluff rice mixture with a fork and let rest covered 10 minutes before serving; garnish with sliced scallions if using. (Optional)