Heat the oil in a pot large enough for the stew ingredients. Fry the ginger strips until browned, then remove them from the pot.
Fry the mustard seeds until they pop. Add the onion and garlic, followed by the chile paste and tomatoes, then the shrimp paste and powdered spices.
When the spices are fragrant, brown the chicken pieces. Add water to just cover the meat, season with salt and sugar and bring to a boil. Cook for 10 minutes.
Add the potatoes and sausages and turn down fire to simmer until chicken is tender. Finally add the cucumber, green chiles and roast pork, if using. Leave for a while for flavors to mature and squeeze in lemon juice just before serving.
