To make the lemon oil, combine the ingredients in a small saucepan and heat over very low heat for 1 hour. Do not let the oil get too hot or start smoking. Remove from the heat, let cool, and strain. Keep refrigerated up to 7 days.
Combine the lemon juice and mustard in a small bowl. While whisking, add the oils in a slow steady stream. Whisk in the honey. Season to taste with salt and pepper. Toss with the greens and onion, and enjoy immediately!