Preheat oven to 400°F (200°C).

Roast the vegetables on a baking sheet on the top rack of the oven.

Heat olive oil in an ovenproof saucepan or Dutch oven over medium-high heat.

Add the chopped onion and cook, stirring, until softened (about 3 minutes).

Add the Arborio rice and stir to coat with oil.

Stir in the white wine and cook until evaporated (about 1 minute).

Stir in 2 cups of hot water, salt, and pepper, and bring to a boil.

Cover and transfer to the oven's bottom rack.

Bake for 25 minutes, or until most liquid is absorbed.

Remove from oven and stir in the remaining 1/2 cup of hot water, butter, and cheese.

Serve topped with the roasted vegetables and shaved Parmesan cheese.