Bring half a large steamer to the boil, tip the potatoes into the water, then lay the salmon fillets, skin-side down, in the steamer basket. Cover and cook for 6-8 mins until the salmon is cooked through, then remove and set aside. Continue to cook the potatoes for another 5-8 mins until tender, adding the beans for the final couple of mins. Drain the veg, then tip into a large bowl.
Add the olives and tomatoes to the potatoes and beans, then gently flake in chunks of the cooked salmon, discarding the skin. Whisk together the garlic, lemon and oil with some seasoning, and loosen with a few drops of water. Pour the dressing over the salad, toss well, and serve.