Preheat your oven to 400°F and line a baking sheet with parchment paper.
Pat the chicken breast dry and season both sides with salt and pepper.
Lightly spray the chicken with olive oil spray. Then, evenly coat the chicken with the panko breadcrumbs, pressing gently to adhere.
Place the chicken breast on the prepared baking sheet and bake for 20-25 minutes, or until the internal temperature reaches 165°F and the coating is crispy.
While the chicken bakes, prepare the herb aioli by mixing the Greek yogurt with the mixed fresh herbs and lemon juice. Adjust salt and pepper to taste.
Once the chicken is done, let it rest for a couple of minutes. Slice the whole wheat bun open and toast lightly if desired.
Assemble the sandwich by spreading the herb aioli on both sides of the bun, then layering lettuce, tomato slices, and the crispy baked chicken breast.
Serve immediately and enjoy your flavorful, crispy baked chicken sandwich!