In a bowl or measuring cup, mix together the soy sauce, cornstarch, sugar, rice wine vinegar, ginger and crushed red pepper flakes.
Heat the oil in a large high-sided skillet or wok over high heat. Add the bell peppers and stir until browned, 1 to 2 minutes. Scoot the peppers to the edge of the pan, creating an opening in the center.
Add the shrimp in a single layer to the center of the pan and cook until just beginning to turn pink, 1 to 2 minutes. Add three-quarters of your scallions (hold back the rest for garnishing at the end) and stir everything together.
Add the kale and cook until wilted, about 2 minutes. Next, pour in the sauce and allow it to bubble and thicken in the pan while stirring, about 1 minute. The sauce should really cling to the shrimp and vegetables. Remove from the heat.
Sprinkle everything with the cilantro and mint and stir to combine. Garnish with more red pepper flakes and the remaining scallions before serving.