Bring water and rice to a boil in a large pot. Cook, stirring constantly, until rice is soft, about 25 minutes.
Heat vegetable oil in a saucepan over medium heat. Cook and stir garlic in the hot oil until golden brown, 5 minutes. Transfer half of the garlic to a small bowl.
Stir ginger into the garlic remaining in the saucepan; cook and stir until fragrant, about 1 minute. Add onion; cook and stir until softened, about 5 minutes. Add chicken; season with fish sauce and pepper. Cook and stir until chicken is no longer pink in the center, about 5 minutes.
Stir chicken mixture into the rice. Dust annatto powder over rice using a strainer; stir until dissolved. Add hard-boiled eggs. Simmer on low, stirring constantly, until rice reaches a porridge-like consistency, about 5 minutes. Remove from heat and stir in spring onions.
Garnish bowls of congee with reserved fried garlic.