Roast the red pepper over an open flame or under the broiler until the skin is charred on all sides. Place it in a bowl and cover it tightly with plastic wrap. After about 20 minutes take the pepper out, cut it in half, remove the core and scrape away the skin and the seeds. Do not rinse under running water. Cut into narrow strips.
Soak the cut leeks in a bowl of cold water.
Put the olive oil and garlic in a 12-inch skillet and place over medium high heat. When the garlic begins to sizzle, add the Belgian endive. Lift the leeks out of the water and add them to the pan. Season with salt and pepper and stir well, then turn the heat down to medium low and cover the pan. Cook, stirring occasionally, until the vegetables are very tender, 20 to 25 minutes.
Fill a pot for the pasta with about 6quarts of water, cover, and place over high heat. When the water boils, add 2tablespoons salt, add the fusilli, and stir well. Cook until al dente.
Uncover the pan with the vegetables, raise the heat to medium high and add the roasted peppers. Cook, stirring often, for 2 to 3 minutes until the peppers are heated through, then remove from the heat and set aside.
When the pasta is done, drain well, toss with the sauce and serve at once.