Preheat oven to 400 degrees F. Place the cauliflower, garlic, and onion slices on a large baking sheet. Drizzle with olive and toss until well coated. Season with salt and pepper, to taste. Roast until golden and tender, about 20 minutes. Remove the pan from the oven and stir the cauliflower. Add the tomatoes and return the pan to the oven. Roast for 10 minutes.
While the cauliflower is roasting, bring a large pot of salted water to boil. Cook the pasta until al dente, about 7-8 minutes. Drain pasta and set aside.
Meanwhile, make the Lemon Caper Vinaigrette. In a small bowl, whisk together lemon juice, olive oil, capers, maple syrup, mustard, and red pepper flakes. Set aside.
Roughly chop the roasted onions. Remove the garlic from the peel and chop.
In a large pan, combine pasta, cauliflower, tomatoes, onions, and garlic. Add the Lemon Caper Vinaigrette and stir until coated. Heat over medium heat until pasta is warm. Serve with shredded Parmesan cheese and season with salt and pepper, if desired.