In a large bowl combine all ingredients for the marinade. Mix well, cover with plastic wrap and marinate in the fridge for up to 2 hours.
In a large pan on medium high heat, saute the onion, ginger, garlic and garam masala in olive oil. Cook for about 5 min until the spice becomes fragrant and the onion softens. Add in the mushrooms and cook until they are soft and have released all their water. Add in the marinated chicken and cook for 5 min. Pour in the curry sauce and simmer for another 15 min, or until the chicken is cooked through.
Serve over basmati rice and top with fresh coriander.