Slow-Cooker Spicy Chicken Curry

Name: Slow-Cooker Spicy Chicken Curry
Prep time: 10 min
Cook time: 4 h
Total time: 4 h 10 min
Cuisine: Asian
Ingredients: 1 tbsp vegetable oil; 1 large onion (peeled and chopped); 3 chicken breasts (boneless and skinless diced (approx 500g/17.5 oz) ); 3 cloves garlic (peeled and minced); 1 large piece of ginger (about the size of your thumb, peeled and finely chopped); 1 tsp salt; ½ tsp ground black pepper; 3 tsp hot chilli powder (use less or mild chilli if you don’t like your curry too hot); 1 tbsp ground coriander; ½ tbsp cumin; 1 tbsp curry powder; 1 tsp paprika; 1 tsp cinnamon; 1 cup (240 ml) chicken stock ( (water plus a stock cube - or bouillon for gluten-free - is fine)); 400 ml (14 oz) tinned chopped tomatoes; 2 tbsp tomato puree (paste for US); 2 tsp sugar (this is to counteract the acidity in the tomatoes); 400 ml (14 oz) can full-fat coconut milk; 2 tbsp cornflour (cornstarch) (mixed with 5 tbsp cold water to make a slurry - *optional*); boiled rice; chopped coriander (cilantro) and finely chopped chillies