In a food processor, create the marinade by blending together the finely chopped lower third of the lemongrass stems, the garlic, shallot, ginger, turmeric, chilli flakes, ground coriander and soy. Place the chicken in a zip lock bag, pour the marinade over and leave for an hour or up to overnight. Remove and pat dry.
To make the green sambal, in a dry frying pan add the green chillies, shallots and garlic. Cook until blackened on all sides, about 10 minutes. Place the chillies in a plastic bag to steam for 2 minutes. Peel the skins off and remove the seeds. Peel the garlic and shallots and place in a food processor with the chillies. Add the fish sauce, sugar and chopped coriander and pulse to a chunky consistency. Squeeze in the lime juice and taste for additional fish sauce. Scrape into a bowl.
Mix all the red sambal ingredients together in a small bowl and set aside.
Preheat your outdoor grill or chargrill pan. Grill the chicken over indirect low heat for 10 minutes each side until charred at the edges and the skin is starting to pull back.
Serve the grilled chicken with the green and red sambals and garnish with shallots and fresh coriander.