Bring a large saucepan of water to a boil. Add 2 cups orzo; cook, stirring occasionally, until just al dente, 5 to 7 minutes. Drain and rinse under cold water until cool.
Meanwhile, whisk lemon zest, lemon juice, ¼ cup oil, ½ teaspoon pepper and ¼ teaspoon salt in a large bowl.
Add the orzo, 4 cups broccoli, the flaked tuna, 1 cup olives and 1 tablespoon oregano to the dressing; stir to combine.
