This lemon orzo soup is bright and lively. Poaching chicken in store-bought broth is an easy way to enrich the soup and provide an extra depth of flavor.
Cook orzo according to package instructions; drain and set aside.
Meanwhile, heat oil in a large pot over medium heat. Add carrots, fennel, and onion; cook, stirring occasionally, until softened, about 5 minutes. Add garlic and cook until fragrant, about 30 seconds. Add oregano and lemon zest; cook for 30 seconds.
Add chicken and broth. Bring to a boil, then reduce heat to a maintain a simmer. Cook until an instant-read thermometer inserted in the thickest part of the chicken registers 165 degrees F, 10 to 12 minutes. Remove from heat; transfer the chicken to a plate to cool slightly. When cool enough to handle, shred or chop the chicken and return it to the soup. Stir in the cooked orzo, along with lemon juice, dill, salt, and pepper.