Heat the vegetable oil in a large skillet over medium-high heat. Add the pork belly and cook until browned and crispy, about 5-7 minutes.
Add the sliced onion, garlic, and ginger to the skillet. Sauté for 2-3 minutes until the onion is translucent.
In a small bowl, whisk together the soy sauce, gochujang, honey, rice vinegar, and sesame oil. Pour the sauce over the pork and onion mixture, stirring to coat.
Add the green beans and red bell pepper to the skillet. Cook for another 5-7 minutes, stirring occasionally, until the vegetables are tender and the sauce has thickened.
Remove from heat and garnish with chopped green onions and sesame seeds before serving.