- Place ½ cup olive oil, basil, parsley, walnuts, miso, parmesan cheese, rice vinegar, and garlic in a food processor and pulse until thoroughly combined.
- Pound chicken breasts to ½ -inch thickness and place in a glass dish. Add 2 tablespoons of pesto and coat chicken breasts. Cover and refrigerate for 30 minutes or up to 8 hours.
- Heat a medium cast-iron grill pan over medium-high heat for 2 minutes or preheat your outdoor grill to medium-high. Brush bread slices with remaining olive oil and grill for 1-3 minutes on each side. Transfer to a plate. Place chicken breasts on hot pan or grill and grill for 6 minutes on each side or until fully cooked.
- To make each sandwich, spread 2 tablespoons of pesto on 2 slices of bread. Top with ½ cup arugula, 1 grilled chicken breast and a few slices of tomato. Place the other slice of bread on top. Serve warm.