Cut the onion into strips, mince the garlic.
In a large pot over a medium flame, heat the oil and add the onion and garlic.
Cook, stirring, until the onions are translucent (be careful not to brown them!).
Cut the peppers into strips, carrots into slices and add to the onions.
Add about a cup of the beef stock and bring to a boil.
Reduce the heat all the way to low, cover the pot and let everything simmer for about an hour (or until very soft).
Cut the chicken breasts into cubes and season according to taste.
In a separate pot, cook the chicken on cooking spray.
Add the chicken to the vegetable stew (add the rest of the stock if it seems dry).
Cut up the tomatoes into cubes, add along with the tomato sauce into the chicken/vegetable mixture.
Season with paprika, salt and pepper to taste.
Let everything simmer for another 30 minutes or so.
Mix the cornstarch with the water and add to the mixture, let it come to a boil.