Preheat the oven to 400°F. Place the bell peppers on a lined baking pan and drizzle with 1 tablespoon olive oil. Season with salt and black pepper. Roast for 20 to 30 minutes, or until tender, turning only a few times during baking. Remove from the oven and set aside to cool slightly.

While the peppers are roasting, add the remaining 2 tablespoons olive oil to a large skillet and heat over medium heat. Add the sliced onions and cook for about 20 minutes, stirring occasionally, until softened and lightly browned. Add the minced garlic and cook for 1 additional minute. Remove from the heat.

Fill a large stockpot halfway with water and bring it to a boil. Add the green beans and cook for 2 to 3 minutes, or until bright green and just tender. Using a slotted spoon, transfer the beans to a bowl of cool water.

Add the spinach to the same boiling water and cook for 1 minute. Remove with a slotted spoon and transfer it to the bowl of cool water with the beans.

Cook the pasta in the same pot of boiling water according to the package directions. Drain the pasta, rinse it with cool water, and drain again thoroughly. Transfer the pasta to a large bowl and toss with a small drizzle of olive oil.

Dice the roasted peppers once they are cool enough to handle. Roughly chop the basil and quarter the tomatoes if not already prepared.

Add the roasted peppers, cooked onions and garlic, green beans, spinach, tomatoes, basil, and Parmesan cheese to the bowl with the pasta. Season with salt, black pepper, and white pepper. Drizzle with a little additional olive oil and toss thoroughly to coat and combine.

Serve immediately, or chill and serve later if desired.