Heat the olive oil in a large skillet over medium heat.
Add the diced onion and bell pepper, cooking until softened, about 5 minutes.
Stir in the minced garlic and cook for an additional minute until fragrant.
Add the ground chicken to the skillet, breaking it up with a spoon. Cook until browned and fully cooked through, about 6-8 minutes.
Sprinkle in the Cajun seasoning, stirring well to combine.
Pour in the tomato sauce, Worcestershire sauce, and brown sugar. Stir to mix everything together and let it simmer for about 5-10 minutes, allowing the flavors to meld. Season with salt and pepper to taste.
While the mixture simmers, toast the hamburger buns if desired.
Spoon the Cajun chicken mixture onto the bottom half of each bun. Top with chopped green onions and place the top half of the bun on each.
Serve immediately.