Chargrilled salmon with sherry and walnut dressing

Ingredients

• 1/4 cup olive oil
• 1 tbsp walnut oil
• 1 lemon (zest finely grated and juiced)
• 1/4 cup medium dry sherry
• 4 salmon steaks (with skin (about 115 grams/4 oz each))
• 2 zucchini (pared into ribbons with a vegetable peeler)
• 5 oz mixed salad greens (such as arugula, lamb's lettuce or baby spinach)
• 1 pink grapefruit (peeled and cut into segments)
• 2 tbsp walnuts (roughly chopped)