Help-yourself tuna rice salad

INGREDIENTS

• approx 900g/2lb cold cooked rice (about 400g/14oz uncooked rice)
• 400g tuna in springwater
• 200g frozen petits pois , defrosted under the hot tap
• 2 red peppers , peeled with a potato peeler, deseeded and diced
• 3 tomatoes , chopped into small chunks
• 5 spring onions , finely sliced
• bunch flat-leaf parsley , chopped
• large handful stoned green olives , roughly chopped (optional)
• 4 tbsp mayonnaise
• juice 1 lemon
• 2 tbsp extra-virgin olive oil