In a pan heat the olive oil, add urad dal and chillies and stir fry for a minute. Add in onions and salt. Then fry all ingredients until it's all mixed well. Then, let the mixture cool completely. Finally add tamarind, brown sugar & grind it to a fine paste.
Separately, season chicken with salt and pepper and allow to marinate at least an hour.
Heat grilling pan with 2 tbsp of oil and cook the chicken slowly and gently for 10 minutes each for both sides or until browned.