Step 1Steam, boil or microwave sweet potato for 8–10 minutes, or until just tender; drain well. Transfer to a bowl, mash roughly with a fork and set aside to cool. Meanwhile, steam or grill fish for 6–8 minutes, or until just cooked through. Set aside to cool, then flake fish with a fork.
Step 2Meanwhile, spray a medium non-stick frying pan with olive oil and set over medium heat. Sauté onion for 5 minutes, or until softened. Add garlic, lemon zest and oregano; cook, stirring for 1 minute or until fragrant. Set aside to cool.
Step 3Meanwhile, place couscous in a medium heatproof bowl. Pour over ¹/³ cup boiling water and stir to combine. Cover couscous and set aside to steam for 3 minutes. Then fluff and separate grains with a fork. Transfer couscous to a large plate.
Step 4Place cooled sweet potato, fish and onion mixture in a large bowl. Season with cracked black pepper and stir until well combined. Using your hands, shape mixture into 8 x 2cm-thick patties. Press each fish cake gently into the couscous to coat on both sides.
Step 5Meanwhile, whisk soy sauce and lemon juice with 1 teaspoon olive oil in a large salad bowl. Add coleslaw and toss to combine; set aside.
Step 6Heat the remaining oil in a large non-stick frying pan over a medium-high heat. Pan fry the fish cakes for 2–3 minutes each side, or until golden brown. Serve fish cakes with coleslaw and lemon wedges.