To cook the cauliflower bring a large pot of water to the boil. Meanwhile, melt the butter in a large skillet set over medium heat. Add the bell pepper, celery, carrot and garlic and cook until tender, about 4 to 5 minutes. When the water is boiling, add the cauliflower and cook until just tender, about 2 to 3 minutes. Drain well, and then add to the skillet with the other vegetables. Season with salt and pepper, add the parsley, gently toss to combine, and serve.