To make the dressing: whisk together the olive oil, lemon juice, zest, garlic, cumin, paprika, salt and pepper until blended.
In a large bowl, toss lettuce with ½ of the dressing. Spoon the remaining dressing over the green beans, potatoes and tuna. Gently coat the ingredients evenly with the dressing. Arrange the lettuce on a large platter. Top with the green beans, potatoes and tuna, and sprinkle with paprika. Serve at room temperature.