Heat the oil in a skillet over medium heat. Cook the chicken in the hot oil until completely browned, 3 to 5 minutes; 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.