Place the portions of salmon fillet, skin side down, in a shallow flameproof dish. The portions should fit snugly in a single layer. Mix the mustard, ginger, garlic, honey and soy sauce or tamari together in a bowl, then spoon this mixture evenly over the fillets. Set aside.
Heat a ridged frying pan, put the courgettes and oil into a plastic bag and toss together, lift out the courgette slices and fry until lightly browned on each side and tender. You may need to do this in batches. Stir the lime rind and juice, mint and seasoning together in a bowl.
While the courgettes are cooking, heat the grill on the hottest setting. Grill the salmon fillets for 10–15 minutes, depending on their thickness, until lightly charred on top and cooked through. Transfer to serving plates, arrange the courgette slices around them and drizzle with the lime dressing. Serve hot.