Slow cooker spicy chicken breasts

Ingredients

• 4 - 5 chicken breasts
• 6 - 7 small tomatoes
• 1 onion
• 1 small can of tomato paste
• 2 jalapeño peppers
• 3 cloves of garlic
• 2 tablespoons vegetable oil
• 1 teaspoon Dijon mustard
• refined sugar, to taste
• 3 tablespoons white wine vinegar
• 1/2 tablespoon Worcestershire sauce
• 2 teaspoons cornstarch
• 1 teaspoon chilli powder
• 1 teaspoon cumin seeds
• 2 teaspoons paprika powder
• 50ml (2 fl oz) water
• salt and pepper to taste