Preheat the oven to 190 °C (375 °F). Place both halves of the squash on a baking sheet, cut side up, and bake for about 60 minutes. Once cooked, take the squash halves out the oven and scoop out the flesh using a fork. Put the squash flesh in a large bowl and add a few tablespoons of butter, then season with salt and pepper to taste. Mix and set aside.
Remove the skin from the duck breasts and then slice each one into two cutlets. Cut each cutlet into cubes, then sauté for 5 minutes over high heat in a large skillet with a little butter. Set aside.
In a 9 x 13-inch (23 x 33 cm) rectangular baking dish, spread a thin layer of sundried tomato pesto and half the diced tomatoes. Cover with a row of lasagna noodles.
Spread another thin layer of pesto over the noodles and cover with the spaghetti squash. Cover with another row of lasagna noodles, then the duck breast cubes and half the green onions. Season to taste with pepper, Italian seasoning and garlic salt. Top with another row of noodles, then the rest of the pesto, spaghetti squash and diced tomatoes. Season to taste again with pepper, Italian seasoning and garlic salt.
Garnish with remaining green onions and grated cheese. Cover the lasagna with a sheet of aluminum foil and place it on the centre rack of the oven. Bake the lasagna for 45 minutes or until the liquid around the edges begins to bubble slightly. You can remove the aluminum foil at the end of cooking and brown the top of the lasagna for a few minutes under the broiler. Remove the lasagna from the oven and let stand for 10 minutes before slicing gently and serving. Serve with your choice of salad.
This lasagna can be made up to two days in advance and stored covered in the refrigerator, making sure to bake it for another 15 minutes.
