Place the chicken breast between two sheets of parchment paper and pound to an even half-inch thickness.
In a shallow dish, whisk together the almond flour, garlic powder, smoked paprika, sea salt, and black pepper.
Press the chicken breast firmly into the almond flour mixture until both sides are thoroughly coated.
Lightly coat the chicken with olive oil and place in an air fryer basket at 375°F for 12-15 minutes, flipping halfway through, until golden and crispy.
While the chicken cooks, whisk together the Dijon mustard, honey, and Greek yogurt in a small bowl until smooth.
Toast the whole grain bun in a dry pan over medium heat until the edges are slightly browned.
Spread half of the honey-mustard sauce on the bottom bun, then layer with the lettuce and tomato.
Place the crispy chicken on top, drizzle with the remaining sauce, and close the sandwich with the top bun.