Preheat oven to 400 degrees F. Cut off top 1/4 of pumpkins. Remove seeds and strings; reserve 2/3 cup pumpkin seeds.
Place pumpkins, cut side up, in foil-lined baking pan. Brush insides with some of the bacon drippings and sprinkle with salt, pepper, and brown sugar. Replace lids. Roast pumpkins in oven 20 minutes.
Meanwhile, in skillet stir together pumpkin seeds, fennel seed, green onions, and remaining bacon drippings. Add skillet to oven during last 10 minutes of roasting.
Remove pumpkins and seed mixture from oven. Sprinkle inside of pumpkins with seed mixture and crumbled bacon. To serve, use a large spoon to scoop out insides or use knife to cut into wedges. Makes 8 to 10 servings.