Using a pastry brush, coat the chicken breast with the marinade. Refrigerate for 30 minutes. Sprinkle the breast with the poultry seasoning. Grill the chicken on direct high heat for 10-12 minutes, turning once during the grilling process.
While chicken is cooking: Heat butter in a medium sauté pan over high heat. Add mushrooms, salt, and pepper and sauté 6-7 minutes, stirring occasionally. Drain excess liquid.
Once the chicken has finished grilling, leave on the grill and rop each chicken breast with one slice of each of the cheeses. Divide onions and mushrooms evenly among the chicken breasts and place atop the cheese. Close the grill lid and cook until the cheese has melted.
Brush the hamburger buns with melted butted and toast on the grill over medium direct heat for 2-3 minutes.
Place the chicken on the hamburger buns, top with the fresh tomato slices and serve.
Yield: 6 sandwiches