Whisk together 2 tablespoons almond flour and cornstarch in a shallow bowl. Whisk together beaten egg white and 2 tablespoons mustard in a second shallow bowl. In a third shallow bowl, combine crushed almonds and remaining 2 tablespoons almond flour.
Dredge chicken cutlets in cornstarch mixture; shake off excess. Dip in egg mixture; let excess drip off. Dredge in crushed almond mixture.
Heat 1 tablespoon oil in a large nonstick skillet over medium. Add chicken; cook until golden brown and cooked through, 5 to 6 minutes per side.
Wipe skillet clean; add remaining 1 tablespoon oil, and increase heat to high. Add cabbage and onion; cook, stirring occasionally, until lightly browned, 3 to 4 minutes. Sprinkle with pepper; transfer to a large bowl. Add grapefruit segments, celery, and parsley; toss to combine. Whisk together grapefruit juice, honey, and remaining 1 tablespoon mustard. Drizzle two-thirds of dressing over slaw mixture; toss. Drizzle remaining dressing over chicken and serve.