Tuna and Avocado Salad

2 x 185 gram tins tuna in oil, drained and flaked
1 x 400 gram tin cooked cannellini beans, drained and rinsed
1 cos lettuce, shredded
12 cherry tomatoes, halved
2 spring onions, thinly sliced
¼ cup picked flat-leaf parsley
2 Lebanese cucumbers cut into long shards, lengthwise
1-2 avocados, sliced into wedges
4 eggs, hardboiled and quartered
½ cup black olives, pitted

Dressing
2 teaspoons Dijon mustard
1 clove garlic, crushed
2 tablespoons lemon juice
4 tablespoons olive oil
sea salt and freshly ground pepper