Soba noodles with sake-poached chicken

20g dried shiitake mushrooms
1/2 cup sake
1/4 cup light soy sauce
1 1/2 teaspoons caster sugar
2 cups chicken stock 
300g chicken breast fillets
1 bunch bok choy or choy sum
270g packet soba noodles
1 red capsicum, thinly sliced 
1 small red chilli, thinly sliced
|Soba