Make the sauce: In a saucepan cook the garlic in the oil over moderately low heat, stirring, until it is just golden. Add the tomatoes, chopping them with a spoon, and stir in the onion, basil, red pepper flakes, oregano, sugar, and salt to taste. Bring the mixture to a boil and simmer the sauce, stirring occasionally, for 45 minutes, or until it is thick and almost all of the liquid is evaporated.
While the sauce is cooking, in a kettle of boiling salted water cook the capellini for 6 to 8 minutes, or until it is just tender, and drain it well. In a non-stick skillet measuring 10 inches across the bottom, heat the oil over moderate heat until it is hot but not smoking. In it cook the bell pepper rings for 30 seconds on each side, or until they are crisp-tender, and transfer them with tongs to a plate. To the skillet add the capellini, distributing it evenly and pressing it lightly. Cook it, covered, over moderate heat for 25 minutes, or until the bottom is golden. Invert an oiled baking sheet over the skillet, invert the capellini "crust" onto the sheet, and slide it back into the skillet. Cook the capellini crust, covered, for 10 minutes more, spread the sauce over it, leaving a 1/2-inch border, and arrange the mozzarella on top. Arrange the bell pepper rings and the pepperoni on the mozzarella and cook the "pizza", covered, over moderate heat for 3 minutes, or until the mozzarella is melted. Slide the pizza onto a pizza pan or flat platter. Garnish it with the basil. With a pizza wheel or sharp knife cut it into wedges.
Recipe courtesy of Gourmet Magazine