Preheat the oven to 400°F.
Heat 2 TBSP oil in a medium Dutch oven over medium-heat. Add 2 TBSP onion, garlic, salt, and pepper. Cook, stirring occasionally, 5-7 minutes, or until transparent.
Add the rice to the dutch oven. Cook, stirring constantly, 1-2 minutes or until the rice begins to smell slightly toasty. Stir in vegetable broth, cover tightly and place in the oven. Bake until rice is tender and cooked through, about 65-70 minutes.
While the rice is cooking, place the butternut squash on a medium, foil-lined baking sheet and toss with 2 TBSP of remaining oil and a bit of salt and pepper. Place in the oven, and roast for 20-25 minutes, until browned and tender. Remove from the oven, let cool slightly.
While rice and butternut squash are in the oven, prepare the caramelized onions and mushrooms. Heat remaining oil and 1 TBSP of butter in a medium skillet over medium-high heat. Reduce the heat to medium-low, and add the onions. Cook, stirring often, 8-10 minutes, or until they begin to caramelize slightly. Add ¼ cup of white wine to deglaze the pan. Continue cooking for another 5 minutes to continue caramelizing the onions. Increase heat back to medium-high and stir in the mushrooms and a dash of salt. Cook, stirring often, 5-8 minutes. Add another ¼ cup of wine to the pan to deglaze once again. Cook for another 4-5 minuts or until mushrooms are tender and onions are caramelized. Remove from the heat and set aside until risotto is ready to eat.
Remove the pot of rice from the oven. Add butternut squash, water, parmesan cheese, remaining wine, remaining butter, and lemon zest. Stir vigorously for 2 to 3 minutes, until the rice is thick and creamy.
Divide risotto among 4-6 wide and shallow bowls. Top with onion and mushroom mixture and more parmesan cheese, if desired.