Preheat oven to 425° F. On a rimmed baking sheet, toss the potatoes with 1 tablespoons olive oil. Season with salt and black pepper. Arrange the lemon halves and smashed garlic cloves around the potatoes. Bake 20 minutes, or until tender. In a shallow bowl, combine 2 tablespoons olive oil, 2 cloves chopped garlic, 2 tablespoons oregano, the paprika, the red pepper flakes, and a pinch each of salt and pepper. Add the salmon and toss to coat. Remove the potatoes from the oven and push them to one side of the pan. Put the salmon on the other side, add a couple pats of butter to each filet. Arrange the lemon slices around the salmon. Return the pan to oven and bake for 10 to 20 minutes, until the salmon reaches desired doneness.To make the dressing. Combine the remaining 1/3 cup olive oil, the parsley, 2 tablespoons oregano, the basil, olives, vinegar, and fish sauce (if using).Remove the garlic cloves from the baking sheet. Finely chop/mash the garlic into a paste, stir the garlic into the dressing. Season with crushed red pepper and salt.To serve, divide the salmon, potatoes, and lemon slices between plates. Gently crumble the feta around the salmon, then spoon the dressing over everything. Add a handful of arugula. Eat and enjoy!