Cook the couscous according to package directions and immediately toss with 1 teaspoon olive oil to prevent clumping. Allow to cool.
On a large platter, arrange the arugula in a row down the center. Make a row of the cooked (yet, slightly cooled or cold) couscous next to it. Sprinkle the couscous with a little salt.
In a small bowl toss the diced tomato with the Parmesan, 1 teaspoon olive oil, balsamic vinegar, salt, and pepper. Make a row of it on the other side of the arugula.
Toast the pepitas in a toaster oven or in a small, dry pan on the stove. They are done when you start to hear a bit of popping. Toss them together with the raisins and place in another row next to the tomatoes.
Cut up the smoked salmon and place it in a row next to the couscous.
To make the dressing, either whisk together the sour cream, buttermilk, lemon juice, basil, and garlic, or for the best results, quickly blend it together with a hand immersion blender. Pour over top and serve.