Cut the chicken thighs into bite-sized pieces. Season with salt and pepper.
Heat the oil in a large pan over medium-high heat. Add the chicken and brown for 5 minutes until golden on all sides. Remove and set aside.
In the same pan, add the onion and cook for 4 minutes until soft. Add the garlic, ginger, curry powder and turmeric. Cook for 1 minute until fragrant.
Add the red lentils, chopped tomatoes and stock. Stir well and bring to the boil.
Return the chicken to the pan. Reduce the heat and simmer for 20 minutes until the lentils have broken down and the sauce is thick.
Stir in the garam masala and season with salt and pepper. Serve with boiled rice and fresh coriander if you have it.