Prepare the pickled red onions by heating the vinegar, sweetener, and water together in a heatproof measuring cup. Heat in the microwave until boiling. Add the red onions and ⅛ teaspoon of salt. Stir to combine and allow to sit and cool until the onions have turned pink throughout.
In the meantime, chop the kale, dice the strawberries and slice the cooked chicken breasts.
Prepare the dressing by whisking the lemon juice, olive oil, the rest of the salt, the black pepper and ½ a grated garlic clove together in a small bowl.
Assemble the salad by placing the chopped kale in the bottom of a large bowl. Top with crumbled goat cheese, then half of the drained pickled red onions and the sliced chicken. Finish with the dressing.