In a large pot, heat the oil on medium-high. Add the onions, celery, and carrots. Season with salt. Cook 6 min., stirring often.
Meanwhile, chop the chicken into ½-inch chunks.
To pot, add the broth and water. Heat to a boil. Add chicken to the pot. Reduce heat and simmer 8 min., stirring occasionally.
Break the pasta into 1-inch pieces and add to pot. Cook 6 min., until pasta is tender and chicken is cooked through, stirring often. Season with salt and pepper. To serve, stir in the dill and lemon juice.