Cube the thighs - try to get even pieces, cooking will be easier.
Prepare a large bowl (marinade) and a small bowl (to cook later), this will save you a lot of prep time.
In both bowls, add : 3/4 tsp garam masala, 1/4 tsp Kashmiri powder, 2 crushed garlic. In the large bowl, add 1 tbsp olive oil, juice of 1/2 lemon, 1 cm grated ginger, and while you're manipulating ginger, roughly chop the second 1 cm piece and add it to the small bowl. Then add 1/2 tsp coriander and 1/2 tsp cumin to the small bowl. Do not add salt. Salt draws out moisture, and you'll get a drier meat.
Store the small bowl, and give a stir to the large bowl. Add cubed chicken to the large bowl (with yogurt if using). Give another stir. Cover the bowl with auto-seal plastic wrap and leave it for 1h (on the counter), or for the night (in the fridge).
Once the chicken has marinated long enough, and you're ready to cook it, soak 68g of cashews pieces, or whole cashews, in boiling water.
In the meantime, heat a large pan on high heat. Sear the chicken pieces until golden, then flip them and sear the other side - do NOT crowd the pan, or its temperature will drop dramatically, and chicken pieces won't be seared properly.
Put the chicken pieces back into the empty marinating bowl.
To deglaze the pan, add the onion (frozen onions work even better). Once their water has disappeared from the bottom of the pan, add the small bowl of spices / ginger / garlic. Sauté for about 30 seconds, until fragrant. Add diced tomatoes, stir and simmer a couple minutes until it thickens.
Turn the heat down to "low" under the pan.
While it's simmering, drain the cashews and add them to a high-speed blender.
Use a laddle to transfer the tomato mixture in the blender. Add coconut milk and mix until smooth and creamy.
Return the sauce to the pan, add the chicken, partially cover with a lid, and simmer for 7-10', until chicken is cooked through.
If you own a meat thermometer, the probe should show an internal temperature of 75°C - 80°C.
While the chicken finishes cooking, sauté some cauliflower rice. Add fried onions and fresh parsley if you like.
And / or cook lentils pasta, regular wheat/rice pasta, or rice, if you're not SCD. Everything goes well with this chicken ;-)
Serve warm with a pinch of salt, and enjoy :-)