Preheat your oven to 375 degrees F. and prepare a large baking dish.
In a large skillet, heat the olive oil over medium-high heat, then add the onions and garlic. Saute for 5 minutes until fragrant then add the diced squash and mushrooms. Add 1-2 tbsp of water then season with a good pinch of salt and pepper and cook for 5 minutes until the vegetables are soft. Remove from the heat.
In a small bowl, combine the ricotta with the spinach, season with Italian seasoning, and mix well.
Cover the bottom of the baking dish with pasta sauce, then add a layer of pasta.
Top with some ricotta sauce and cooked vegetables, then add another layer of pasta and top with pasta sauce. Repeat this step, until all ingredients are used.
Cover the baking dish with foil and bake in the preheated oven for 40-50 minutes. Remove the foil and let the lasagna rest for 15 minutes before slicing. Garnish with fresh basil leaves and enjoy!