Marinading the chicken: In a large bowl, combine the chicken pieces with the garam masala, cumin, ground coriander, turmeric, and a pinch of salt. Mix well to coat the chicken evenly. Cover and let it marinate for at least 30 minutes (or overnight in the fridge for better flavour) Making the curry:Spritz the pan with some cooking spray. Add the chopped onions and cook until they are soft and translucent, about 5-7 minutes.Add the crushed garlic and cook for another 1-2 minutes until fragrant. Add the marinated chicken, chopped bell peppers, and sliced mushrooms.
Pour in the chopped tomatoes, tomato puree, smoked paprika, and chilli powder. Stir everything together until well combined.
Cover and cook on low for 6-7 hours or on high for 3-4 hours, until the chicken is cooked through and tender.
About 30 minutes before serving, stir in the low-fat Greek yogurt and reduced-fat coconut milk. Mix well and let it cook without the lid for the remaining time. Taste and adjust seasoning with salt and pepper if needed.
If you find the curry a little too watery try simmering on the hob for a few minutes to remove some of the moisture.