Preheat an outdoor grill or indoor grill pan to medium. In a medium skillet, heat 2 tbsp. EVOO over medium-high heat. Add the peppers, chiles and onion and cook until crisp-tender, 5 to 6 minutes. Add the garlic and bay leaf; season with salt and pepper. Cook for 2 minutes, then stir in the sugar. Add the sherry to deglaze. Stir in the tomatoes, lower the heat and simmer.
In a saucepan, bring the chicken stock, 1 tbsp. EVOO and the butter to a boil. Add the couscous and scallion whites, then remove from the heat and cover for 5 minutes. Fluff the couscous with a fork and add the scallion greens, mint and parsley.
Brush the fish with EVOO and season with seafood seasoning blend, if using (otherwise, use sea salt and pepper). Grill, turning once, for 6 minutes.
Discard the bay leaf from the peppers. Top the fish with the peppers and serve the couscous alongside.