In a small skillet over medium heat, melt the butter. Stir in the sugar until it dissolves, then add the walnuts and ground cinnamon.
Cook, stirring constantly, until the walnuts are lightly toasted and well coated, about 2 minutes. Move walnuts to a plate to cool.
Whisk together the olive oil, apple cider vinegar, honey, salt, and black pepper in a small bowl.
Sprinkle the walnuts over the salad. Serve immediately.