1. In a Dutch oven or large heavy pan, heat the canola oil over medium-high heat. Saute the onions, bell pepper, and garlic for about 4 minutes, until soft. Remove pan from heat.
2. Put the flour in a large sealable plastic bag. Add chicken and shake the bag to coat chicken with flour evenly. Remove the chicken pieces, shaking off excess flour, and add them to pan. Cook chicken over medium heat for 4 minutes, stirring frequently, until all the pieces are opaque and the flour has colored and slightly browned in places.
3. Stir in rice. Add the tomatoes, broth, thyme, salt, cayenne, and black pepper. Bring the liquid to a boil, reduce heat, cover and simmer 30 minutes.
4. Add mushrooms, arranging them on top of the rice mixture. Pour in the water. Return mixture to a boil, reduce heat to low and cover partially. Simmer for 20 to 30 minutes or until the rice is done. Stir in scallions and quickly remove pan from heat. Let cool for about 5 minutes and serve.