Place sweet potatoes on a baking sheet, and bake at 375° for 50 minutes or until very tender. Let cool, and peel.
Combine sweet potatoes, molasses, gingerroot, salt, and pepper in a bowl; beat at medium speed of a mixer until smooth. Set aside.
Heat oil in a large nonstick skillet over medium-high heat. Add squash and next 6 ingredients (squash through onion); sauté 8 minutes. Add broth; bring to a simmer, and cook 20 minutes, stirring occasionally.
Spoon squash mixture into a 3-quart casserole. Spread sweet potato mixture evenly over squash mixture. Bake at 375° for 35 minutes; sprinkle with pecans, and bake an additional 15 minutes.