For Pho Ga, first roast the shallots, onions and ginger under the grill until light brown.
Heat the broth, add the grilled shallots, onions and ginger and bring everything to a boil. Reduce the heat, add the fish sauce, salt and sugar and simmer for 1 hour. Pour the soup through a sieve and keep hot.
Blanch the chicken breast in boiling water until the meat is cooked and then cut it into thin strips. Cook the noodles in boiling water until just tender. Drain the noodles and place them in a bowl.
Spread the chicken over the cooked noodles, pour the soup over them and serve Pho Ga sprinkled with spring onion and coriander.