For the Dressing: In a measuring cup or jar, combine lemon juice, olive oil, harissa, preserved lemon, cilantro, and pepper. Stir or shake until well combined; season with salt. Set aside.
For the Salad: In a large bowl, combine rice, tuna, olives, scallions, bell pepper, and green beans. Using two big forks, toss gently until well combined and rice grains are separated.
Drizzle with the dressing and toss gently, fluffing the rice, until evenly dressed. Garnish with cilantro leaves, if using. Serve at room temperature.
