Seafood couscous paella

Ingredients

• 1 teaspoon vegetable oil
• 1 onion, finely sliced
• 1 red pepper, finely sliced
• 4 tomatoes, roughly chopped
• 200g giant couscous
• Pinch of saffron (optional)
• 1 teaspoon paprika
• 100ml reduced-salt vegetable stock
• 600ml boiling water
• 100g frozen peas
• 150g cooked king prawns
• 150g cooked mussels
• Freshly ground black pepper
• 2 teaspoons lemon juice
• 1 lemon, cut into wedges, to serve