Heat the oil in a large pan, then add the onion. Cook very gently for about 10 mins. Stir in the garlic and ginger and cook for a further 1 min.
Add the spices and cook for 1 min, then add the chicken, squash and red pepper. Fry in the spices for about 3 mins.Tip in the tomatoes and stock, then simmer for 25-30 mins until the sauce has thickened and the chicken is cooked through.
Meanwhile, cook the basmati rice according to the pack instructions.
Stir the spinach into the curry to wilt, then add the garam masala, if using (leave out if you want a milder curry).
Add the yogurt and cook for 1 min, then serve with the rice.
Cook's tip: to freeze, cook the curry to the end of step 5. Set aside to cool completely, then freeze for up to 1 month. To serve, defrost overnight in the fridge before reheating until piping hot throughout. Finish with the yogurt and serve with cooked rice.