Boil water with salt in large pot, add Lasagne noodles and soften. Do not over cook - they will finish cooking in the oven.
While boiling water, slice up your leeks, mushrooms, onion and dice your red bell pepper. Saute with butter until soft.
In large bowl, whisk ricotta cheese, pesto sauce, and sauteed veggies. This will be filling
Preheat oven to 375
Peel and then slice the sweet potatoes. 1/8th inch thick or thinner.
Lightly oil baking dish, bottom and sides.
Lightly cover bottom of dish with spaghetti sauce
Layer 3 noodles, overlapping slightly
Then cover with 1/4th the ricotta, then light sauce, layer light mozzarella then a layer of sweet potatoes
Lightly salt each layer of sweet potatoes as you layer them, repeating 2-3 layers total
Top layer add the remaining 3 pasta. Tuck them in the edges. Then sauce them and add a healthy portion of mozzarella cheese evenly. Cover with foil.
Bake covered for 50 minutes. Bake on a cookie sheet so juice does not spill over into oven,
Carefully remove foil and make an additional 10-15 minutes at 400 degrees until the top is brown. Let cook for a few minutes, and slice 3x4 squares and serve.