Make Macadamia flour: mix together flour, pulverized nuts and season with salt and fresh black pepper. Make egg dip for chicken breast: mix one egg with milk and 1 tablespoon mustard, and season with salt and fresh black pepper. Make mustard sauce: mix remaining mustard and mayonnaise, and thin with water.
Slice the chicken breasts in 3 horizontal slices. Pound them slightly between plastic wrap or waxed paper, season with salt and pepper. Slice the onion thinly, saute it in 1 tablespoon olive oil for about 4 to 5 minutes until caramelized. Remove from pan.
Flour chicken pieces and dredge in the egg dip, then flour them again. Saute them for 3 minutes on each side until golden brown. Remove from pan to a baking sheet and bake them at 375 degrees for 3 to 4 minutes, or until juices run clear. Drain excess oil and breading from the saute pan, and add 1 tablespoon olive oil and sliced garlic. Stir until golden. Add spinach and red pepper, sauteeing until spinach is wilted. Season with salt and pepper, and transfer to the center of a serving plate. Add 1 tablespoon butter to the pan. When melted, add the onions and cook briefly. Place on top of the spinach. Remove the chicken from the oven and fan it around the vegetables. Spoon the mustard sauce around it