Gluten-Free Chicken Sandwich with Creamy Green Goddess Dressing

For the Green Goddess Mayonnaise:

• 1
  cup
  mayonnaise
• 2
  teaspoons
  anchovy paste or 4 anchovy fillets
• 1
  cup
  chopped fresh herbs,
  any combination of chives, dill, parsley, or basil
• 1
  tablespoon
  lemon juice
• 1/2
  teaspoon
  garlic powder

For the Sandwiches:

• Olive oil
• 4
  boneless,
  skinless chicken breasts, halved lengthwise and pounded very thin
• Kosher salt and freshly ground pepper
• 16
  slices
  gluten-free bread,
  toasted (we like Canyon Bakehouse)
• 1
  (16-ounce) ball fresh mozzarella, sliced into 8 slices
• 1
  cucumber,
  peeled and thinly sliced
• 1
  head butter lettuce,
  leaves separated
• 1
  (4-ounce) package sprouts (such as alfalfa, broccoli, or pea)

1. Make the green goddess mayonnaise: In a food processor or blender, combine the mayonnaise, anchovy paste (or fillets), chopped herbs, lemon juice, and garlic powder. Blend until the mixture is smooth and pale green. Taste and adjust seasoning if needed. Chill until ready to use; extra mayo will keep in an airtight container in the refrigerator for up to 2 days.
2. Make the sandwiches: Preheat a grill pan or an outdoor grill on high. Drizzle olive oil over both sides of each chicken breast, season generously with kosher salt and freshly ground pepper, and grill until golden and cooked through, about 2 to 3 minutes per side depending on thickness. Transfer the chicken to a cutting board to rest; halve pieces that are too large to fit on the bread. Toast the gluten-free bread if desired. Spread about 1 tablespoon of green goddess mayonnaise on each slice of bread. On eight slices, layer a piece of chicken, a slice of mozzarella (or omit for dairy-free), cucumber slices, a few butter lettuce leaves, and some sprouts. Top with the remaining bread slices, mayonnaise side down, and press gently. Wrap in parchment for easy transport or serve immediately.