Begin by bringing a large pot of salted water to a rolling boil over high heat. Once boiling, add the orzo and cook according to the package instructions, usually around 8–10 minutes, until al dente. Drain and rinse under cold water to cool.

In a large mixing bowl, combine the diced red and orange bell peppers, chopped red onion, cucumber, corn, halved tomatoes, chopped basil, and sliced green onions. Toss gently to mix.

In a small bowl, whisk together the olive oil, lemon juice, lemon zest, Dijon mustard, minced garlic, salt, and pepper until smooth and well combined.

Add the cooled orzo to the vegetable mixture. Drizzle with the dressing and toss everything together until fully coated.

Serve chilled or at room temperature, optionally topped with freshly grated Parmesan cheese. If made ahead, cover and refrigerate for up to four days.