Char peppers and onion on a grill or under a broiler, then peel and seed peppers. Puree peppers and onion.
Poach chicken breasts by bringing to a boil in a pot of water, reducing heat and simmering for 20 minutes. Drain and cool, then shred into bite-sized pieces.
Saute mirepoix (leeks, celery, carrot and garlic) in oil over medium-low heat until vegetables soften. Add flour and stir through thoroughly. Stir in cumin seed, then sherry and broth, pressing out any lumps of flour. Season with salt and pepper and simmer for 30 minutes.
Add pepper puree and simmer 10 minutes more. Add chicken and cream and heat through without boiling.
Cut tortillas into 1/4" strips and fry quickly in a bit of vegetable oil; drain and salt. When crisp, sprinkle on bowls of soup to serve.
Notes
Make ahead and refrigerate or freeze for your offshore cruise.