Soak the cedar plank: Submerge the cedar plank in cold water for at least 1 hour (up to 3 hours) before grilling. Soaking prevents the wood from catching fire and creates steam that imparts a subtle smoky aroma into the fish.

Prep the peppers for charring: Place whole red and yellow peppers under a broiler or directly over a gas burner and char until the skins are blackened on all sides, turning with tongs. Charring develops a sweet, smoky complexity and separates the skin from the flesh so you can peel it away.

Steam and peel the peppers: Transfer charred peppers to a bowl and cover tightly with plastic wrap (or place in a sealed paper bag) for 10–15 minutes to steam — this loosens the skins and makes peeling easy without losing the smoky flavor.

Make the pepper relish: Peel and seed the peppers, then chop coarsely and transfer to a mixing bowl. Add the minced shallot, 1 tbsp olive oil, 1 tbsp lemon juice, capers (1 tsp per serving; 4 tsp total), minced garlic, half of the chopped parsley and mint (reserve the rest for the couscous), and a generous pinch of salt and cracked pepper. Stir and taste; the acid from lemon brightens the charred sweetness and capers add briny pop. Refrigerate while you cook the fish to let flavors meld.

Prepare the couscous: Bring 350 ml (about 1 1/2 cups) water to a simmer with 1/2 tsp salt and 1 tbsp olive oil. Remove from heat, stir in the 280 g (about 1 1/3 cups) instant couscous, cover, and let sit 5 minutes until the grains swell. Fluff with a fork and stir in the remaining chopped parsley and mint, 3 tbsp lemon juice (reserve 1 tbsp for finishing fish), and 2 tbsp olive oil; seasoning now ensures the couscous absorbs bright, herby flavor instead of tasting bland.

Season the swordfish: Pat the 680 g total (4 × 170 g) swordfish steaks dry with paper towels — dryness is key to a good sear. Brush both sides lightly with the remaining oil (about 1 tbsp) and season generously with kosher salt and cracked black pepper. A light oil layer prevents sticking to the plank and pulls heat to the surface for a golden crust.

Preheat the grill: Heat the grill to medium-high (around 400–450°F / 200–230°C). Remove the cedar plank from the water and pat the top dry (keep the underside damp). Preheating the grill ensures the plank and fish heat quickly, producing immediate sizzle and good sear without overcooking.

Oil the plank and place on the grill: Lightly oil the top of the plank to prevent sticking, then place it on the hot grill for 2–3 minutes to begin releasing smoke. You should see thin wisps of smoke; this primes the plank for flavor infusion.

Grill the swordfish: Lay the seasoned swordfish steaks on the hot cedar plank. Close the grill lid and cook 4–6 minutes per side depending on thickness; for 170 g steaks (roughly 1-inch thick) aim for about 5 minutes per side. Cooking on the plank allows low, even heat transfer; the brief closed-lid grilling traps smoke and moisture so the fish stays tender. Cook to an internal temperature of 130–135°F (54–57°C) for medium (carryover will raise it a few degrees during resting).

Rest the fish: Transfer the steaks to a warm plate and rest 4–6 minutes. Resting allows the juices to redistribute and the internal temperature to settle, yielding a moist swordfish steak rather than a dry one.

Finish and plate: Spoon a generous portion of the charred pepper relish over each swordfish steak, then serve alongside 70 g (uncooked) couscous portion (cooked as prepared). Drizzle 1 tsp lemon juice per steak (from the reserved tablespoon) and a light drizzle of olive oil, then finish with a sprinkling of the remaining chopped herbs for color and freshness. The hot fish with room-temperature relish creates a pleasing textural and temperature contrast.

Optional garnish and final seasoning: Add a few extra capers on top for briny bite and a pinch of flaky sea salt if desired. Taste one forkful and adjust with more lemon or pepper if it needs brightness.