These pearled couscous stuffed peppers are a great option for a weeknight dinner, but are also elegant enough for guests. The filling and vinaigrette can be prepped a day ahead; store both, covered in the refrigerator. Gently reheat the filling before stuffing and baking the peppers as directed. Bring the vinaigrette to room temperature before serving.
Preheat oven to 400 degrees F. Toss peppers with 2 tablespoons olive oil, a few pinches of salt, and black pepper. Roast, cut sides up, for 15-20 minutes, until softened.
While peppers are roasting, prepare the couscous. Heat 2 teaspoons of olive oil in a pot until shimmering. Add couscous, and cook, stirring, for about 2-3 minutes, until pearls begin to toast. Add 1/2 teaspoon salt, water, and bring to a boil. Cover, reduce heat, and simmer for 8-10 minutes, until water is absorbed and couscous is tender. (Alternately, follow the cooking directions as provided for the brand of couscous you buy.)
While couscous is simmering, heat 2 tablespoons of oil in a large skillet over medium-high heat until shimmering. Add shallots, and cook until softened, about 3-5 minutes. Stir in garlic and cook until fragrant, about 1 minute. Add baby spinach and 1/2 teaspoon each of kosher salt and pepper. Stir until spinach is wilted and tender, about 2-3 minutes. Remove from heat.
Stir cooked couscous into spinach mixture, followed by 1/2 cup Parmigiano Reggiano. Gently fold in cannellini beans. Season to taste with salt and pepper.
Drain any accumulated juices from the roasted peppers and fill each half with couscous mixture, mounding slightly, and pressing gently to pack. Sprinkle peppers with remaining Parmigiano Reggiano, and return to the oven to bake until cheese is melted, about 5-7 minutes.
Whisk together 1/4 cup olive oil, 2 tablespoons lemon juice, 1/2 teaspoon lemon zest, and 2 tablespoons chopped chives. Season vinaigrette to taste with a few pinches of salt and pepper.