Grilled Greek Potato Salad Recipe

3 pounds small red potatoes, halved 2 tablespoons olive oil 1/2 teaspoon salt 1/4 teaspoon pepper 1 large sweet yellow pepper, chopped 1 large sweet red pepper, chopped 1 medium red onion, halved and sliced 1 medium cucumber, chopped 1-1/4 cups grape tomatoes, halved 1/2 pound fresh mozzarella cheese, cubed 3/4 cup Greek vinaigrette 1/2 cup halved Greek olives 1 can (2-1/4 ounces) sliced ripe olives, drained 2 tablespoons minced fresh oregano or 1 teaspoon dried oregano