Preheat the oven to 350 degrees. Lightly spray a 9- or 10-inch springform pan with gluten-free nonstick cooking spray. Cut a circle of parchment paper to fit the bottom of the pan, place in the pan and spray it lightly with more cooking spray.
Peel and core the pears. Chop three of the pears roughly and slice the fourth into about ¼-inch slices. Take the chopped pears and put in a small, microwavable bowl with the lemon juice and 2 teaspoons of Swerve. Cover and microwave on high power for 4 minutes. (Alternatively, you can cook on the stove for 10 minutes over medium heat in a covered saucepan.) Mash the pears into a coarse puree with a fork or wooden spoon. Let cool.
Put the almond meal and 1¾ cups of Swerve in a food processor and give it 4 or 5 long pulses. Add the eggs, vanilla extract, and the cooked pears and puree the mixture. Pour into the prepared pan.
Sprinkle the sliced almonds over the top of the cake. Add the pear slices in a spoke configuration.
Bake for 45-55 minutes or until the cake is nicely browned and a toothpick inserted into the center comes out clean. Check the cake after about 35 minutes; if it is browning too much, place a piece of foil over the top.
Let the cake cool in the pan for about 30 minutes, then remove the sides of the pan and transfer to a serving platter. Dust with Swerve Confectioners and serve with whipped cream, if desired.