Preheat the oven to 425°F. Spray an 8x8x2-inch baking dish with cooking spray, and set aside.
Combine the onion, garlic, and water in a microwave-safe bowl. Season with salt and pepper to taste. Cover the bowl tightly with plastic wrap, and microwave on high for 10 minutes. Pour the mixture into a blender and blend it until it is completely smooth.
Bring a large pot of salted water to a boil. Add the macaroni and cook according to the package directions. In the last 2 minutes of cooking, add the broccoli florets; drain.