Heat vegetable oil in a saucepan and fry onion till soft and translucent. Then add chopped ginger, dry red chili, and curry leaves and fry till onion turns light golden.
Now add chopped tomato and fry for a few minutes till it combines well with onion and oil starts to separate.
Add marinated chicken pieces and cook for 2 minutes on high heat followed by the Chettinad masala paste, lemon juice, and salt if needed. Stir well, cover, and cook till the chicken is fully done. Add water only if needed in small quantities, but it is better not to add any water at all.
Finally, add chopped coriander leaves and cook for 1 more minute.
Turn off the heat and remove the curry in a serving dish.
Heat some coconut oil and add curry leaves. Cook for a few seconds and pour this tadka over the chicken curry.
Serve hot with rice or Kerala parotta or naan.