Preheat a grill or griddle pan over medium-high heat. Season the fish with the Old Bay and drizzle with EVOO.
Using a food processor, finely chop the chile, garlic, mint, cilantro, parsley, paprika, cumin and coriander; season with salt and pepper. Add 1/4 cup olive oil and the lemon or lime juice and peel; pulse into a thick paste.
In a large saucepan, melt the butter. Add the zucchini and cook over medium-high heat for 5 minutes; season with salt and pepper. Add the chicken stock and bring to a boil. Stir in the couscous, cover and turn off the heat. Let stand for 5 minutes, then fluff with a fork.
Grill the fish, turning once, until firm, 6 to 8 minutes. Transfer to a platter, spread with the chermoula sauce and let stand for 5 minutes to absorb the flavors. Serve with the couscous.