How to Make It
Preheat oven to 350ºF. Bring a medium saucepan of salted water to a boil. Stir in orzo and cook until just tender, about 8 minutes or according to package instructions. Drain and rinse under cold water until cool. Drain well and transfer to a bowl. Stir in olives, 1 Tbsp. basil, 1 tsp. oil and 1/4 tsp. each salt and pepper. While orzo is cooking, if using pine nuts, spread them on a small baking sheet and bake, stirring once, until golden and fragrant, 5 to 8 minutes. Transfer to a small bowl and let cool.
In a medium bowl, whisk together vinegar, mustard, 1/2 tsp. pepper and a pinch of salt until well combined. Slowly add remaining 2 Tbsp. oil in a stream, whisking until emulsified. Fold in 1 cup tomatoes, bocconcini, remaining 2 Tbsp. basil and shallot.
Layer salad evenly between 2 1-quart-capacity containers, beginning with tomato mixture, then adding orzo, remaining 1 cup tomatoes, arugula and pine nuts. Cover containers. Salads will keep, covered and refrigerated, for 2 days. Let containers sit at room temperature for at least 20 minutes before serving. Shake container before eating to distribute ingredients.