Slow Cooker Chicken Curry

Name: Slow Cooker Chicken Curry
Cuisine: Asian, Indian
Ingredients: 1 tbsp sunflower oil; 1 tbsp garam masala; 8 chicken thighs, boneless & skinless; 250ml chicken stock; 400g tin chopped tomatoes; 1 red pepper, diced; Sea salt; For the spice paste; 1 onion, finely chopped; 3 cloves garlic, peeled & sliced; 1 large thumbsized piece ginger, peeled & sliced; Small handful fresh coriander, stalks & leaves; 1 tbsp turmeric; 1 tbsp ground cumin; 1 tbsp ground coriander; 1 tbsp ground ginger; 1/2 tsp chilli powder; Pinch of freshly ground black pepper; To serve; Juice of ½ lemon; A small handful of coriander leaves, to garnish; 250g basmati rice, cooked