Preheat the oven to 400°F (200°C). Arrange the halved bell peppers on a parchment-lined baking sheet. Drizzle with 1 tablespoon of olive oil and season with salt and black pepper. Roast for 20–30 minutes, stirring once or twice, until tender and slightly caramelized. Add the minced garlic during the final minute of roasting. Set aside to cool slightly before dicing.

In a large skillet, heat the remaining 2 tablespoons of olive oil over medium heat. Add the sliced onions and cook for approximately 20 minutes, stirring occasionally, until deeply browned and softened. Remove from heat and set aside.

Fill a large stockpot halfway with water and bring to a boil. Add the chopped green beans and cook for 2–3 minutes, or until bright green and tender-crisp. Using a slotted spoon, transfer them to a bowl of ice water. Repeat this process with the spinach, blanching for about 1 minute before transferring to the same bowl. Drain both well.

In the same pot of boiling water, cook the pasta according to the package directions until al dente. Drain and rinse briefly under cool water to stop the cooking. Toss with a small amount of olive oil to prevent sticking.

In a large serving bowl, combine the cooked pasta, roasted peppers, caramelized onions, blanched green beans and spinach, cherry tomatoes, and chopped basil. Drizzle with additional olive oil and season with salt, black pepper, and a pinch of white pepper if using. Add the shaved Parmesan and toss thoroughly until all ingredients are evenly coated.