Three bean salad with salmon

1 large can (14.75 oz.) salmon
8 ounces tender green beans, halved
1 cup canned cannellini beans, rinsed and drained
1 cup canned pinto beans, rinsed and drained
1/2 cucumber chopped into chunks
12 cherry tomatoes, halved
6 green onions, finely sliced
Bunch young, fresh spinach leaves or watercress
3 tablespoons olive oil
2 tablespoons lemon juice
2 teaspoons grainy mustard
Salt and freshly ground black pepper
Drain and chunk salmon, removing skin and bones (if any). Cover and set aside. Cook green beans in lightly salted boiling water 4-5 minutes, until just tender. Rinse with cold water and drain well. Transfer to salad bowl; add cannellini and pinto beans. Add cucumber, cherry tomatoes, green onions and spinach. Toss together to mix; add salmon chunks and toss again gently.

Mix together olive oil, lemon juice and grainy mustard. Season with salt and pepper. Pour over salad just before serving, tossing gently to combine with ingredients.