Heat a medium-sized sauce pan over medium-high heat, add the green onions and ginger to the pan, stir until fragrant but no color. Season the chicken breasts with salt and add to the pan.
Add the water and stir to combine. Poach the chicken until cooked, about 3-4 minutes, skimming the surface of the broth as the chicken cooks.
Remove the chicken breasts from the liquid; allow to rest at room temperature. Once cool enough to handle, shred the chicken meat with your hands, or two forks.
Remove the green onion from the broth. Add in tofu, shredded chicken, chicken soup powder, and lemon juice and zest. Season soup with salt and white pepper to taste.
When ready to serve, divide soup into four bowls; garnish with the lemon slices, green onions, and fresh coriander.