1. Combine shallot and vinegar in a small bowl and set aside. Mix mayonnaise, herbs, and garlic in a medium bowl and season to taste with pepper. Transfer 3 tablespoons herby mayo to a second small bowl, cover, and refrigerate.
2. Place chicken breasts between two sheets of plastic wrap and gently pound to a 1/2" thickness, then halve crosswise to make four similar-size cutlets. Season with salt and pepper.
3. Place panko in a shallow bowl. Brush cutlets all over with remaining 2 tablespoons herby mayo. Working with one cutlet at a time, coat chicken in panko, turning and pressing firmly to adhere. Transfer to a plate and repeat with remaining cutlets.
4. Line a large clean plate with paper towels and set aside. Heat oil in a large nonstick skillet over medium heat until shimmering. Add cutlets and cook, flipping once, until panko is golden brown and thickest part of chicken registers 165 degrees, 3 to 5 minutes per side. Transfer to prepared plate.
5. Add shallot-vinegar mixture to reserved herby mayo and stir to combine. Add arugula and toss to coat, then season with salt and pepper to taste. To assemble sandwiches, place a cutlet on each bun bottom, top evenly with arugula mixture and a bun top, and serve.
Source: Hannaford fresh Magazine, March - April 2020