Heat canola oil in a large saucepan set over medium heat. Add apples, green onions and ginger and cook, stirring frequently, until apple begins to soften, 8 to 10 minutes.
Add garlic and saute for 30 seconds.
Turn heat to medium-low and add Patak's curry paste and cook, stirring frequently, about 5 minutes.
Turn heat back to medium and add chicken thighs and ½ cup water. Cook, turning chicken frequently, for 10 minutes.
Add coconut milk and turn chicken to coat.
In a small bowl, stir together cumin, coriander and 4 teaspoons water to make a paste. Stir into the curry. Add cayenne pepper, if desired. Season with salt.
Add potatoes, cover pot with lid ajar, turn heat to low to medium-low and simmer for 1 to 2 hours, or until chicken is cooked through and the gravy thickens.
Serve with basmati rice, naan, raita, mango chutney and diced cucumbers, tomatoes and bananas.