In a medium bowl, whisk together honey, soy sauce, minced garlic, apple cider vinegar, black pepper, and red pepper flakes (if using). Set aside.
Heat vegetable oil in a large skillet over medium heat. Add the sliced sausages and cook until browned, about 5-7 minutes.
Pour the honey garlic sauce over the browned sausages in the skillet. Stir to coat the sausages evenly.
Reduce heat to low and let the mixture simmer for 10-15 minutes, stirring occasionally, until the sauce thickens slightly.
Remove from heat and garnish with chopped green onions before serving.