Place the chicken, taco seasoning mix and water into a resealable plastic zipper bag, seal and massage the bag with your fingers to mix. Refrigerate for 30 minutes to marinate.
Cut the stem and top 1cm from the top of each capsicum and carefully remove the seeds without cutting holes or breaking skin of the capsicums. Bring a large pot of water to boil and immerse the capsicums in the boiling water for 3 minutes; cool immediately in a bowl of cold water. Drain the capsicums and set aside.
Heat the vegetable oil in a large saucepan over medium heat; cook and stir the onion until translucent, about 5 minutes. Stir in garlic, oregano, cumin and cinnamon; cook for 3 minutes. Stir in the flour and chilli powder and cook for about 1 minute.
Whisk in the chicken stock and bring the mixture to a boil stirring constantly until the sauce thickens, about 5 minutes. Reduce heat to low and stir in the chocolate until it melts and blends into the sauce. Allow the sauce to gently simmer, stirring occasionally.
Drain the marinated chicken breasts and place into a frypan over medium heat. Cook until the chicken is no longer pink inside, about 10 minutes; remove chicken to a bowl and set aside to cool.
When cool enough to handle shred the chicken meat and lightly mix in a bowl with cheese, cream cheese and coriander. Stuff each capsicum with 1/4 of the chicken mixture and place on their sides on a baking tray.
Preheat the grill and set the oven rack about 15cm from the heat source. Grill the stuffed capsicums until blistered and hot, about 4 1/2 minutes per side. Serve with sauce.