Make the coriander aioli. Reserve a few coriander leaves for garnish and place the rest in a small food processor or blender with the garlic, mustard, egg yolk and vinegar. Blend until finely chopped. With the motor running, slowly drizzle in the oil until the mixture is smooth and thick. Season with salt and pepper.
Scatter the crushed peppercorns over the chicken slices and drizzle with oil. Cook, in batches, on a preheated hot griddle for 1–2 minutes on each side or until cooked through and golden.
Serve the warm chicken slices with mixed green salad leaves, grated beetroot and the coriander aïoli. Garnish with the reserved coriander leaves.