Bring 1½ cups of salted water and 1 tablespoon olive oil (optional) to a boil. Add the couscous, cover, and remove from the heat. Let sit, covered, until the all the water has been absorbed, 6 to 8 minutes. Fluff with a fork and set aside.
While the water heats and the couscous cooks, prepare the vegetables.

• Cut the leek into 1/4-inch half moons and rinse to remove the grit.
• Finely chop the garlic.
• Zest and juice the lemon.
• Chop the dill leaves.
• Rinse the beans.

In a frying pan over medium-high heat, warm 2 tablespoons oil until hot but not smoking. Add the leeks and garlic, season with salt, and cook, stirring occasionally, until the leeks are beginning to soften and caramelize, 5 to 6 minutes.
Add the shrimp and paprika. Season with salt and pepper and cook, stirring occasionally, until the shrimp is pink and just cooked through, 2 to 4 minutes. Gently stir in the beans and 1/2 cup water and cook, stirring occasionally, until the beans are just heated through and the liquid has reduced by half, 2 to 4 minutes.
Remove the pan from the heat, stir in the lemon zest, lemon juice, dill, and arugula. Season with salt and pepper, if necessary.

Transfer the couscous to individual bowls and top with the shrimp, white beans, and arugula.