Place all ingredients for the cucumber salad in a large sealable Tupperware. Shake to combine and set in the refrigerator until you're ready to assemble.
Slice both chicken breasts in half horizontally. Place flour (season the flour if desired) in one bowl, whisked eggs in a second, and then crush the cornflakes in a third bowl. Dip each breast in flour, then the eggs, then into the crushed cornflakes. Make sure to press the cornflakes onto the chicken so they are fully coated,
Preheat air fryer to 385F. Place the chicken breasts on air fryer tray and spray the top with olive oil cooking spray. Cook for 7 minutes, flip over and spray the other side with cooking spray, and continue to cook for another 7 minutes.
While the chicken is cooking, whisk all ingredients together for the maple-miso mayo mustard sauce and set aside.
Cut the baguette into four equal-sized sandwiches. Cut in half. To assemble, drizzle the bottom half of each sandwich with desired amount of the maple-miso mayo mustard sauce. Then place the crispy chicken on top. Equally divide the cucumber salad among four sandwiches and then drizzle with more of the sauce. Place on the top buns and enjoy sandwiches immediately.