Place 2 skinless, boneless chicken breasts in a medium saucepan and cover with water. Bring to the boil, then reduce to a gentle simmer and cook for 15-20 minutes until cooked through.
Remove the chicken from the pan, reserving 240 ml of the cooking liquid. Leave the chicken to cool slightly, then shred it using two forks.
Tear 5 slices of white sandwich loaf into pieces and place in a bowl. Pour over 240 ml evaporated milk and leave to soak for 5 minutes until softened.
Heat 1 tablespoon olive oil in a large frying pan over medium heat. Add 1 large yellow onion and cook for 5-7 minutes until translucent. Add 4 garlic cloves and cook for a further minute until fragrant.
Stir in 120 ml aji amarillo paste, 1 teaspoon ground turmeric and ½ teaspoon ground cumin. Cook for 2-3 minutes, stirring constantly.
Transfer the onion and paste mixture to a blender. Add the soaked bread and milk, plus the 240 ml reserved cooking liquid, and blend until smooth.
Pour the sauce back into the frying pan and bring to a gentle simmer over low heat, stirring to prevent it from sticking. Add the shredded chicken, 50 g grated Parmesan cheese and 30 g chopped walnuts, then stir to combine.
Simmer for 5-10 minutes until the sauce thickens. Season to taste with salt and freshly ground black pepper.
Serve the chicken stew over cooked white rice and garnish with the 2 halved hard-boiled eggs and 50 g black olives.