1. Combine soy sauce, brown sugar, tahini and chili-garlic sauce in a small bowl.
2. Cook soba according to package directions; drain and rinse under cold water.
3. Heat oil in a stockpot over medium-high heat. Add cabbage, garlic and ginger; saute 5 minutes. Add chicken broth and bring to a boil. Add shrimp, soba and soy sauce mixture and simmer over medium heat until shrimp are just cooked through, about 2 minutes. Garnish with scallions.