In a large bowl, combine the endive, toasted walnuts, and apple slices. Crumble the bleu cheese on top. Add as much as you like (I do about a 1/4 cup), but remember that it has a strong flavor.
In a small bowl, squeeze the juice from one Meyer lemon. While whisking, start adding olive oil (about 1/4 C) and whisk until emulsified. Add a pinch of sea salt and some black pepper. Add a small squeeze of honey or agave. Taste. Add more if necessary. Finish seasoning to taste with salt and pepper. Pour the vinaigrette over the salad and gently mix to combine. Serve.