Heat 1 tsp of the oil in a small saucepan then add the onion and garlic and cook, stirring, for 5 mins until soft.
Stir in the red lentils, chicken stock, tomatoes and curry powder. Cook over a medium-high heat, uncovered, for 10 mins. Reduce the heat to low, and cook with the lid on for a further 20 mins.
Meanwhile, in a separate pan, heat the remaining oil over a medium heat and add the chicken. Cook for 5-10 mins, until cooked through.
Leave the lentils to cool slightly then add the cooked chicken and stir through until combined. Serve immediately.