Saute: Heat the oil in a pot. Chop the onion finely and cook until translucent, about 3-4 minutes, stirring. Add the tomato paste and stir for 1 minute. Add the frozen peas, cover barely with chicken stock, and bring to a boil. Cook for about 10 minutes.
Cook chicken: In the meantime, chop the chicken breasts into cubes. Add them to the pan and cook everything for 5 minutes or until the chicken is cooked through. Don't overcook the chicken.
Thicken sauce (optional): If you want to thicken the sauce (optional), mix the cornstarch with 1-2 tablespoons cold water to obtain a paste. Make a little space in the middle of the pan by pushing the peas away as much as possible and pour the cornstarch paste in a thin stream while whisking all the time with a small whisk. Stir everything very well and let bubble for 1 minute.
Adjust the taste with salt and pepper. Add the finely chopped dill.
Serve with mashed potatoes.
Leftover chicken (or turkey) can be used instead. Alternatively, you can pan-fry or roast chicken drumsticks and serve them with the pea stew.