To make the chermoula paste, toast coriander seeds, cumin seeds and fennel seeds in a dry pan until fragrant, about 5 minutes. Remove from heat and crush in a mortar and pestle. Place into a food processor along with remaining chermoula ingredients and blitz until a paste. Season well with salt and pepper.
Combine cherry tomatoes, red onion, capsicum, garlic and olive oil in a baking dish and season well with salt and pepper. Roast until onion is soft and slightly caramelised, about 20 minutes. Remove from oven and toss with chickpeas, olives, capers, lemon zest and chilli. Set aside.
Season fish with salt. Heat a drizzle of oil in a large oven-proof pan over high heat. Fry fish on one side until just browned, about 1 minute. Flip over and top each fillet with chermoula paste, then place in the oven until fish is just cooked through, about 5 minutes.
Toss herbs through warm chickpea salad and divide between plates. Top with chermoula fish filets and wedges of extra lemon.