First lets make the mashed potatoes. Peel potatoes, chop them up and take them in a sauce pan, cover with water and season with salt. Cook them till it is completely done. Now strain them and add it to the same pan, now mash it well and add in butter, milk, salt and pepper to taste and some nutmeg. Fold it gently till it is smooth. Set aside.
For the veggies, boil carrots and beans in some salted water for 4 to 5 mins. Now strain it and toss it with a tab of butter. Set aside.
Now slice the chicken breast in half in the middle and season it with salt and pepper. Heat oil in a pan, add in chicken breast and cook for 3 to 4 mins on a medium high heat. Remove this to a plate and keep it warm.
In the same pan, add in some butter and add in garlic and fry for a min.
Now add in white wine or water and deglaze the pan. Add in mustard and mix well.
Now add in cream, salt and pepper and mix well. Place the chicken over the sauce and simmer for a min.
Now plate the dish, spoon some mashed potatoes in a plate, place couple of chicken breast and spoon the sauce over, and place some veggies.