Whisk together olive oil, lemon juice, maple syrup, and salt and pepper in a large bowl.
Add the penne, capers, parsley, onion, olives, tomatoes, bell pepper, tuna, and arugula to the dressing and toss well.
I recommend serving the salad immediately. Double the dressing if you want to make it ahead of time, keep the salad well chilled and add the extra dressing just before serving. I’d also recommend adding the arugula last-minute, else it will wilt.