Line a baking sheet with a silicone mat or parchment paper.
In a small pot, bring the maple syrup and butter to a boil. Cook for 2 minutes. Add walnuts. Cook, stirring with a wooden spoon, until the sugar crystallizes (becomes grainy) on the nuts. Remove from the heat.
Immediately spoon on the baking sheet. With a spatula, quickly spread the nuts. Season lightly with salt. Let cool completely. Roughly crush with a knife.
In a vinaigrette blender, shake all the ingredients until the dressing is creamy. Season with salt and pepper.
In a bowl of cold water, let the onion soak for 5 minutes to mellow out the flavour. Drain.
In a large bowl, combine the lettuce, apple, and onion. Add dressing to taste and toss well. Sprinkle with the walnuts and bacon.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.