In a large skillet, heat the olive oil over medium heat. Add the sliced kielbasa and cook until browned, about 5-7 minutes. Stir occasionally to ensure even cooking.
Add the sliced bell peppers and onion to the skillet. Cook for an additional 4-5 minutes, or until the vegetables are tender.
Stir in the minced garlic and cook for 1 minute until fragrant.
In a small bowl, whisk together the honey, soy sauce, apple cider vinegar, black pepper, and red pepper flakes (if using). Pour this mixture over the kielbasa and vegetables in the skillet.
Reduce the heat to low and let the mixture simmer for 5-7 minutes, allowing the sauce to thicken slightly. Stir occasionally.
Serve the honey garlic kielbasa over cooked rice or quinoa, and garnish with chopped green onions.