Whisk together oil, juice, vinegar, and salt and pepper to taste. Set aside.
Bring water to a boil over high heat in a medium saucepan. Add couscous and reduce heat to a high simmer. Cook for 2-3 minutes, or until couscous is tender. Drain and rinse under cold water until cool.
In a medium bowl, mix papaya, cucumber, basil, and mint. Stir in couscous and add dressing. Blend gently.