In a small bowl, combine the cornstarch, water, tamari or soy sauce, and sriracha. Add the ginger and garlic, mix well, then set aside.
Heat 1 teaspoon of coconut oil in wok or large skillet over medium-high heat.
Line a plate with paper towels.
Add the shrimp to your wok and cook, stirring constantly, for about 2 minutes. Once they are pink and barely opaque, remove to the prepared plate.
Add the remaining 1 teaspoon of coconut oil to the wok, then add the cabbage, red bell pepper, and scallion whites. Stir-fry until cabbage is crisp-tender, about 3 minutes.
Stir the cornstarch mixture, then add it to the wok along with the shrimp.
Cook, stirring constantly, until sauce has thickened and shrimp is coated, about 2 minutes.
Remove from heat, garnish with scallion greens, and serve.