• 2 skinless, boneless chicken breast halves
• ¼ cup olive oil
• 2 tablespoons white wine vinegar
• 1 lemon, juiced
• 4 sprigs fresh dill, chopped
• 1 tablespoon garlic and herb seasoning blend (such as Mrs. Dash)
• 1 teaspoon ground black pepper
• 2 tablespoons butter
• 2 tablespoons olive oil
• ⅛ teaspoon garlic powder
• ⅛ teaspoon salt
• 8 thick slices French bread
• 2 tablespoons mayonnaise, or to taste
• 4 slices tomato
• 4 lettuce leaves

Directions

1. Preheat the grill to medium-high heat.
2. Prick chicken breasts all over with a fork, then place in a large bowl. Add 1/4 cup olive oil, white wine vinegar, lemon juice, dill, garlic and herb seasoning, and black pepper to the bowl. Stir to coat chicken breasts thoroughly. Let stand for 10 minutes.
3. Remove chicken breasts from marinade; discard marinade.
4. Cook chicken on the preheated grill until no longer pink in the center and juices run clear, 10 to 15 minutes per side. An instant-read thermometer inserted into the center of a breast should read at least 165 degrees F (74 degrees C). Transfer chicken to a cutting board; let stand for 5 minutes, then cut chicken breasts in half.
5. Melt butter and 2 tablespoons olive oil in a skillet over medium-high heat. Sprinkle garlic powder and salt over butter and oil. Add French bread slices to the skillet; toast until golden brown on one side, about 3 minutes; remove from the pan.
6. For sandwich assembly, place 1 French bread slice, toasted-side down, onto a serving plate. Spread mayonnaise on bread; top with a tomato slice, then season with salt and pepper. Cover with a grilled chicken breast half and lettuce leaf. Spread untoasted side of another French bread slice with mayonnaise and place on top to make a sandwich.