Chicken Stroganoff

This is an adaption of a recipe I found in 'Symply Too Good to be True', by Annette Sym's. It is a great way to make Stroganoff without using sour cream, which is hard to find and expensive in Japan. I was really surprised how much it tasted like the real thing. I thought the gherkins would taste odd, but they matched really well.
Ingredients:
500g chicken breast, chopped and skinned
1 onion, sliced
1 green capsicum, sliced
1/2 red capsicum, yellow capsicum, sliced
1 cup mushrooms (I use Shimeji Japanese mushrooms whole)
375ml can evaporated light milk (In Japan you can't get light, but evaporated milk is sold in smaller cans, I just use one. If I don't have any I just use low fat milk)
2 tbsp tomato paste or 1/2 cup tomato puree
1 tsp chicken stock powder
1 tbsp paprika
2 gherkins, finely chopped
1 tsp crushed garlic
1 tbsp cornflour
salt and pepper
Coat chicken in salt and pepper and fry in olive oil, add onion and garlic until softened. Add mushrooms and capsicums, cook a further 2-3 minutes. Add gherkins, chicken stock powder, tomato paste, paprika and stir well. Add 1/2 cup - 1 cup of water to the pan and stir. Bring to the boil, then simmer. Finally add can of milk and stir, heat but do not boil. Season with salt and pepper. Add cornflour stirred in water to thicken if desired (I like it without).