Place the pieces of apples and pears in a large slow cooker.
Sprinkle with the lemon juice and toss gently to coat thoroughly.
Cut the vanilla bean in half and scrape the seeds into the slow cooker and toss in the pods (or add 1 teaspoon vanilla bean paste).
Add the brown sugar, cinnamon stick, ginger, cardamom, cloves, and nutmeg. Toss gently to coat.
Cover the slow cooker and set to low heat. Cook for about 6 hours or until the apples and pears are completely tender.
Remove and discard the cinnamon stick and vanilla pods. Use an immersion blender to carefully puree the apples and pears to desired smoothness or transfer the mixture to a stand blender and puree.
Serve immediately or refrigerate in an airtight container for up to 3 days.