Preheat the oven to 350 degrees . Place each pear on its side and cut off a 1/2-inch-thick horizontal slice; reserve the slices. Using a melon baller or a spoon, scoop out the core and discard. Hollow out the pears, leaving a 1/2-inch-thick shell. Coarsely chop half of the removed pear. Sprinkle half of the lemon juice over the hollowed-out pears and the chopped pear.
In a medium skillet, heat the olive oil over medium heat. Add the sausage and fennel seeds and cook, breaking up the sausage, until cooked through, about 5 minutes. Using a slotted spoon, transfer the sausage to a bowl. Return the skillet to the heat, add the chopped fennel bulb, figs and chopped pear and cook until softened, about 5 minutes. Stir in the remaining lemon juice. Add to the sausage. Stir in half of the fennel fronds.
Arrange the pears snugly in a baking dish and stuff with the sausage mixture. Top with the pear slices, cover with foil and bake until the pears are soft, 25 to 30 minutes. Set aside the pear tops and divide the brie among the stuffed pears. Bake, uncovered, until the brie melts, about 3 minutes. Top with the remaining fennel fronds and set the pear tops back into place.