Combine the pork, ketchup, vinegar, soy sauce, monk fruit, and five spice powder in a glass bowl and toss to combine. Cover and refrigerate overnight.
Heat a large pan over high heat and add the oil, bell pepper, and onion. Season with a bit of salt and cook, stirring occasionally on high heat. Cook until vegetables are lightly charred and soften slightly, about 5 minutes. Transfer to a serving bowl and set aside. Do not clean the pan.
Add the marinated pork to the now empty pan and cook on high heat until the pork pieces are cooked trough and the sauce reduces and thickens, about 8-10 minutes. Sprinkle with glucomann powder and add the chicken stock. Continue to cook for another 2 minutes, or until the sauce is thickened and coats the pork well. Add back the vegetables and toss in sauce, adding more water or stock, if needed. Season to taste with salt and serve.