Wash the potatoes, put them into a pot. Pour water until potatoes are covered. Add salt and bring to a boil.

Cover the pot and simmer over medium heat until done - a fork can easily be poked through them. Drain water from potatoes, peel and slice them into 3/4 inch slices. Set aside.

Heat oil in a pot over medium heat. Add the mushrooms and sauté for 15 minutes. Add the green pepper and zucchini; and sauté for 5 minutes.

Add the pesto sauce, salt and pepper. Cook uncovered until vegetables are tender and almost all liquid is absorbed. Adjust seasonings.

Meanwhile prepare the White Sauce or Bechemal Sauce (if it looks too thick, add a little more milk). Set the sauce aside.

Lightly grease an 8 x 11-inch baking dish.

Arrange the potato slices in the baking dish. Then spread the vegetable mixture over the potatoes. Pour the white sauce all over the vegetable mixture.

Top with cheese.

Place the baking dish on the middle rack of the oven. Broil on low heat until cheese is melted and the top begins to get lightly browned, about 3-5 minutes.

Remove from the oven and let cool for a few minutes before serving.