In a small dry skillet, toast sesame seeds over medium-high heat, shaking often, until lightly browned and aromatic, about 1 minute. Transfer to a small bowl and set aside. In a large pot, combine chicken broth, garlic and ginger; bring to a boil over high heat. Add rice, reduce the heat to medium-low and simmer until the rice is tender, 12 to 15 minutes. Stir in soy sauce and sesame oil; add chile paste to taste. Add chicken and heat just until warmed through. Ladle the soup into bowls and garnish with scallions and the reserved sesame seeds.