Combine ginger, garlic, scallions, fennel, shredded chicken, broth, and red pepper flakes in a slow cooker. Stir in 2 cups of water, then season with a big pinch of salt. Cook on high for 2 to 3 hours or on low for 4 to 5 hours.
Stir in lemon juice. Add more salt to taste.
Serve soup with soba noodles or rice, and a good drizzle of chili crisp.
Rebecca Firkser is a freelance food writer and recipe developer. Her work has appeared in a number of publications, among them Food52, TASTE, Edible Manhattan, Extra Crispy, The Strategist, and Bon Appetit's Healthyish. She contributed recipes and words to the book "Breakfast: The Most Important Book About the Best Meal of the Day." Once upon a time, she studied theatre design and art history at Smith College, so if you need a last-minute avocado costume or want to talk about Wayne Thiebaud's cakes, she's your girl.