Roasted Sweet Potatoes With Couscous And Tuna

Serving

100g couscous 1 tbsp butter 170ml water 250g sweet potatoes, peeled and cubed 2 tbsp extra-virgin olive oil 1/2 a Japanese cucumber, thinly sliced 150g canned tuna, drained 1 onion, thinly sliced 30g red capsicum, diced 3 pieces pitted kalamata olives, chopped 3 pieces black olives, chopped Freshly squeezed juice of 1 lemon Salt and freshly-ground black pepper