Remove tops and seeds from peppers; partially cook in small amount boiling salted water, about 5 minutes; drain.
Prepare rice according to package directions; mix with chicken, celery, onion, and pimiento.
Combine mayonnaise, salad dressing and seasonings; add to rice mixture and toss lightly.
Fill peppers and place in greased 10x6x 1 1/2-inch baking dish; pour small amount of water around peppers.
Bake in moderate oven (350°) about 30 minutes or till peppers are tender.