You can find farro in most grocery stores, near the rice. If you can't find farro, you can use wheat berries or brown rice instead; cook according to package directions.
Heat a large skillet or grill pan over medium-high heat. Brush chicken with oil. Sprinkle with cinnamon and 1/8 tsp. salt. Cook, flipping once, until the chicken is browned and an instant-read thermometer inserted in the thickest part registers 165 degrees F, about 10 minutes.
Meanwhile, combine farro, cauliflower, green and red peppers, broth, lemon juice, and the remaining 1/4 tsp. salt in a medium saucepan. Cover and cook over medium heat until heated through, about 8 minutes.
Serve the chicken over the farro and vegetables. Sprinkle with mint and pine nuts. Serve with lemon wedges, if desired.
To toast pine nuts, cook in a small dry skillet over medium-low heat, stirring constantly, until fragrant, 2 to 4 minutes. Transfer to a small plate and let cool.