1. 1. In a bowl, mix Worcestershire sauce, onion powder, fine sea salt, and black pepper.

2. 2. Marinate the boneless chicken breast in the mixture for at least 30 minutes.

3. 3. Preheat the grill to medium-high heat.

4. 4. Grill the marinated chicken breast until fully cooked, about 6-8 minutes per side.

5. 5. While the chicken is grilling, sauté sliced green peppers and onions in a pan until tender and caramelized.

6. 6. Toast the hamburger buns on the grill or in a toaster until lightly golden.

7. 7. Assemble the sandwich by placing the grilled chicken breast on a bun and topping it with sautéed green peppers and onions.

8. 8. Serve hot and enjoy your delicious Grilled Chicken Sandwich!