Whisk together garlic powder and next 7 ingredients (all of the seasonings). Season chicken on both sides with some of the seasoning mixture. Reserve the rest of the seasoning, you'll use it a later step.
Drizzle a large pan or skillet with oil and brown chicken over medium heat (about 2-3 minutes on each side). Transfer to a plate and cover to keep warm.
Add orzo, mushrooms, sundried tomatoes, and remaining seasoning mixture to the pan. Stir over medium heat 2-3 minutes until fragrant and orzo is browned. Stir in chicken broth.
Add chicken to the pan (on top of the orzo and mushrooms), cover and cook over medium-low heat for about 20 minutes until liquid is absorbed, orzo is tender, and chicken is cooked through.
Top with fresh-squeezed lemon juice and garnish with fresh herbs (such as oregano and rosemary) if desired and serve hot.