Heat oil in a heavy-bottomed sauté pan until browned on all sides. Remove from pan and reserve. If possible, transfer to an oven-appropriate brazier.
Add onion and green pepper to the pan. Sauté until soft but not browned. Stir in the flour to make a roux. Cook for a few minutes, and then add Hungarian paprika. Stir to combine evenly. Stir in the chicken stock and the tomatoes. Bring to a boil. Sauce will be very thick at this point. Season with salt and pour over chicken in brazier. Cover brazier and cook in 325°F oven for about 30-40 minutes, or until chicken is tender. Remove chicken from sauce and reserve.
Remove any fat that may be present on top of sauce. Temper and add sour cream to sauce. Simmer a few minutes, but do not allow sauce to boil. Adjust seasonings as needed with salt and pepper. Serve with chicken over spaetzle, egg noodles, or rice.