Preheat oven to 400°F. Line 2 large baking sheets with foil and set aside.

Cook orzo according to package instructions. When pasta is done, remove from heat, transfer to serving bowl, and set aside.

In a bowl, combine fennel, tomatoes, olives, 1 tablespoon oil, and 1/4 teaspoon pepper. Mix well and toss to coat evenly. Transfer to a prepared baking sheet and arrange in a single layer. Roast uncovered until edges of fennel start to brown and vegetables soften, about 20 minutes.

Meanwhile, while vegetables are roasting, prepare chicken. In the same bowl, combine remaining 1 tablespoon oil, remaining 1/4 teaspoon pepper, oregano, salt, and 1/4 cup lemon juice. Mix well. Add chicken breasts and toss to coat evenly. Place seasoned chicken breasts in a single layer across a prepared baking sheet and roast uncovered, about 15 minutes or until chicken reaches a temperature of 170°F when a meat thermometer is inserted in chicken breast.

As soon as vegetables are cooked, remove from heat and add to cooked orzo. Mix well. Stir in remaining 1 tablespoon lemon juice and season with salt and pepper to taste. When chicken is done, serve over equal amounts vegetable-orzo mixture.