In a medium saucepan combine rice, 3 tsp of the Cajun seasoning, ½ tsp of the salt, and 2½ cups water. Bring to boiling; reduce heat. Cover and simmer 40 to 45 minutes or until rice is tender and liquid is absorbed. Remove from heat; let stand, covered, 5 minutes.
Meanwhile, in a small bowl stir together onion, lemon juice, and ¼ tsp of the salt. Press down on onion so as much as possible is covered with juice. Cover; let stand 30 minutes.
For sauce, soak cashews in enough very hot water to cover 15 minutes; drain. Place cashews in a blender or mini food processor. Drain onion, reserving soaking liquid. Add soaking liquid to blender with cashews. Add the remaining 1 tsp Cajun seasoning, the tomato paste, and ¼ cup water. Cover and blend until smooth, scraping sides as needed.
In an extra-large skillet cook carrots and celery over medium 4 to 6 minutes or until crisp-tender, stirring frequently and adding water, 1 to 2 Tbsp. at a time, as needed to prevent sticking. Add beans, okra, garlic, and ¼ cup water. Bring to boiling; reduce heat. Cover and simmer 4 to 6 minutes or until vegetables are tender. Stir in bell pepper, the remaining ¼ tsp salt, and the black pepper; cook and stir 1 minute.
Spoon rice into four shallow bowls. Top with bean mixture, drained onion, and parsley. Drizzle with sauce.
