Preheat the oven to 425°F and line a baking sheet with foil. Toss Brussels sprouts, butternut squash, and carrots with olive oil, salt, and pepper. Roast for 25 minutes, stirring once.
Add red pepper for the last 8-10 minutes. In a large pot, bring broth and water to a boil. Melt 2 tbsp butter in a dutch oven, add onion, salt, and cook until softened (5-7 mins). Add garlic, cook briefly, then add rice and toast for about 3 minutes until the edges become translucent.
After adding wine and cooking for 2-3 minutes, add tomatoes. Then, ladle in 5 cups of simmering broth to the rice, cook for 15-20 minutes until most liquid is absorbed, stirring only a few times.
Add 3/4 cup of remaining broth, remove from heat, and mix in roasted veggies and some mozzarella balls. Stir in 2 tablespoons butter, season with salt and pepper. Serve on platters and top each serving with mozzarella balls.