To contain the umami in the ingredients, use a lid that fits the pan tightly and avoid opening it as much as possible. Simmering the ingredients with the tight lid will help to extract the water from the vegetables, keeping the amount of dashi stock and seasonings to a minimum. In addition, the extracted water contains the umami of the vegetables so that will make the dish more delicious.
When making Nikujaga, beef is often used in the Kansai region, but people in the Kanto region tend to use pork instead.