Bring 1 cup of the chicken broth and 1 cup water to a boil over high heat, covered, in a 2-quart saucepan.
Reserve the remaining chicken broth.
Add the rice, cover, reduce the heat to simmer and cook, covered, 17 minutes.
While the rice cooks, if the chicken is frozen, run it under hot water so you can remove any packaging.
Place the breast halves on a microwave-safe plate and microwave 2 minutes, uncovered, on high, to begin defrosting.
While the chicken defrosts, heat the oil in a 12-inch, extra-deep, nonstick skillet over medium heat.
Meanwhile, peel and coarsely chop the onion, adding it to the pan as you chop.
Add the mushrooms to the pan and stir from time to time.
Cut the chicken into bite-size (about 1-inch) cubes.
Add the chicken and the sherry to the pan.
Rinse and seed the bell pepper.
Cut it into bite-size pieces.
Add them to the pan.
Raise the heat to medium-high.
While the chicken cooks, add the basil, onion powder, mustard, paprika, garlic powder and black pepper to the skillet. Cook, stirring frequently, just until the chicken is no longer pink in the center, about 6 minutes.
In a small jar that has a lid, combine the flour with 1/4 cup of the chicken broth.
Reserve the remaining chicken broth.
Shake well to remove any lumps and set aside.
When the chicken has cooked, add the remaining chicken broth and half-and-half to the pan.
Reduce the heat to medium, and stir well.
Shake the flour-broth mixture again and add it to the pan.
Stir well to combine, and continue to stir until the mixture thickens, about 1 to 2 minutes.
Do not let the mixture boil.
Season with salt to taste.
Serve at once over hot rice.