Fry the diced chicken pieces in oil and season with a little salt and pepper. Then set this pan aside for the time being.
Put some oil in another pan to fry the vegetables. Cut the peppers into small cubes and the mushrooms into slices and the spring onions into rings. Use only the upper, green half of the onions. Grate the two cloves of garlic and set them aside for now.
Put all the vegetables in the pan with the hot oil and fry over medium heat. When the vegetables are done after approx. 10-15 minutes, add 1 tablespoon (heaped) tomato paste together with salt and pepper and mix well.
Finally add the fried chicken cubes and the garlic cloves. Mix everything together well and simmer over medium heat for about 5 minutes. Stir every now and then and season to taste. It can be seasoned if necessary. After the 5 minutes take it off the stove and let it rest.
For the puree, cut the potatoes into small cubes and boil them with salted water. Drain and drain the cooked potatoes and put them back in the pot. Add the milk, butter and a little salt and puree with a potato masher.
Divide the hot mashed potatoes on 4 plates and form a hollow in the middle. The chicken sauté is then placed in this. Serve warm.