For the sauce, in a mixing cup, combine the hoisin sauce, soy sauce, rice vinegar, and sesame oil. Stir well and set aside.
Preheat broiler.
Arrange the sliced rounds of grapefruit on a broiler-safe pan. Sprinkle each grapefruit slice with coconut palm or brown sugar. Broil for 5-7 minutes or until sugar is melted. Remove from oven and set aside.
In a large pot, over medium heat, add the vegetable oil, grated ginger, and minced garlic. Stir together and cook for 2 minutes. Add the sliced green onions and cook for another 2 minutes.
Add the raw shrimp to the pot and cook for 5-7 minutes or until the shrimp is cooked through and pink. Timing depends on the size of your shrimp. Once the shrimp is cooked, remove it from the pot using a slotted spoon, place it in a large bowl, and set aside.
Add the thinly sliced savoy cabbage to the pot. Stir well to incorporate all the bits at the pot's bottom. Adjust heat as needed to prevent burning. Cover the pot and let cook for 5 minutes. Remove the lid and stir well. The savoy cabbage should be wilted but still firm. Cook until desired tenderness.
Add only half of the hoisin sauce mixture to the cooked cabbage, and stir to combine.