Cut the onion into thin slices, then cut slices in half.
Peel the potatoes, cut into large bite-sized chunks of approximately the same size, and rinse well.
Add potatoes to a pot of cold water to cover by 1 1/2 inches, bring to a boil, and boil at medium-high heat. Test after 15 minutes for doneness - they should be easily pierced with a fork.
Remove when done, drain, and place in a serving bowl or dish.
Add onions and toss.
To make the dressing, in a small bowl, combine olive oil, lemon juice, lemon zest, garlic, capers, salt, and pepper with a whisk.
Mix the dressing into the salad and serve hot or at room temperature.