Step 1Peel or cut off the squash skin, remove the seeds and strings, and cut the meat in 1-inch pieces. If using fresh tomatoes, halve and seed them, reserving the juice. Drain canned tomatoes, reserving the juice. Chop the tomatoes.
Step 2Heat the oil in a large, deep, heavy saucepan or stew pan. Add the onion and cook over medium heat until golden, 7 minutes. Add the garlic and tomatoes and cook uncovered for 5 minutes. Add the squash, water, salt to taste, 1/4 teaspoon pepper, cinnamon, ginger and sugar. Stir and bring to a boil. Cover and cook over low heat, occasionally stirring gently, until the squash is tender, about 30 minutes.
Step 3If the sauce is too sweet, add 1 to 2 tablespoons of the reserved tomato juice. Taste and add nutmeg and more salt, pepper, cinnamon, ginger or sugar if you like. If the sauce is too thin, uncover and cook over medium heat until it thickens, 2 or 3 minutes. Serve hot.