Melt butter in a large skillet over medium heat. Add ginger, garlic, and onion. Cook until garlic begins to brown, about 5 min.
Add squash, coconut milk, and green beans to skillet. Bring to a boil over high heat, then reduce heat to medium, cover, and simmer for 30 minutes until squash is tender, stirring occasionally. Stir in shrimp and tofu, then season to taste with salt, pepper, and sugar.