Heat the oil in a frying pan over medium heat. Cook the chicken in the hot oil until completely browned, 3 to 5 minutes, then transfer to a slow cooker. Add the onion to the chicken; season with salt and pepper. Place the pears and asparagus atop the chicken mixture.
Mix the garlic, balsamic vinegar, apple juice, rosemary, ginger and sugar together in a bowl; pour over the asparagus. Season again with salt and pepper.
Cook on Low for 4 to 6 hours.
You can use fresh beans instead of asparagus if you like.