Sweat onion, garlic and ginger in oil in large stock pot over medium-low heat until softened. Stir in curry powder and peanut butter.
Slowly stir in stock, then sweet potatoes. Increase heat to high and bring to a boil. Reduce heat to low, cover and cook until potatoes are almost tender, about 5 minutes. Stir in cabbage and cook until cabbage is tender crisp, about 10 minutes.
Stir in tomatoes and beans. Adjust seasoning. Bring stew to a boil.
Mix cornstarch with cold water until smooth. Slowly stir in enough cornstarch mixture until stew reaches your desired level of thickness.
Garnish as desired.