Heat oil in a large pot over medium heat. Add onion and cook until translucent, about 3-4 minutes. Add toasted rice flour and cook one minute, stirring constantly. Add bell peppers, celery and garlic, and saute another 2 minutes. Add water, tomatoes, Onion Garlic Puree, snow crab legs, Old Bay seasoning, Cajun seasoning, and crabmeat (reserve some large lumps for serving), and bring to a boil. Reduce heat and simmer for 1 hour. Add langoustine, shrimp and parsley and simmer another 30 minutes.