Pat the chicken cavity dry with paper towel. Combine the soy sauce and mirin in a small bowl. Brush inside the chicken cavity. Place the sliced ginger and spring onion in the cavity. Place the chicken, breast-side down, in a slow cooker. Pour in enough cold water to cover the chicken completely. Cook on low for 6 hours or until the chicken is cooked through. Reserve the poaching liquid.
Meanwhile, to make the chilli sauce, place the chilli, garlic and salt in a mortar and gently pound with a pestle until a paste forms. Add the ginger, lime juice and soy sauce and stir to combine.
Heat the 2 tsp of peanut oil in a large saucepan over medium heat. Add the garlic and grated ginger. Cook, stirring, for 1 min or until fragrant. Stir in the rice. Add 2 cups (500ml) of reserved poaching liquid and bring to the boil. Reduce heat to low and cook, covered, for 11 mins or until liquid is absorbed and rice is tender. Set aside, covered, for 5 mins to rest.
To make the spring onion sauce, combine the spring onion and ginger in a small heatproof bowl. Combine the peanut oil and sesame oil in a small saucepan over high heat. Heat until very hot. Carefully pour the hot oil over the onion mixture. Stir in the mirin.
Cut chicken into portions, or discard bones and coarsely shred, if desired. Arrange on a serving platter with the cucumber and coriander. Serve with the rice, chilli sauce, spring onion sauce and extra soy sauce, if desired.