In a small sauce pan on high heat combine the apple cider vinegar, water, salt and peppercorns and bring to a boil. Place the thinly sliced red onion in a bowl and once the liquid is boiling, pour it into the bowl. Let the onions marinate for at least 20 minutes.
Creamy Dill Dressing
Combine all of the dressing ingredients in a blender and blend until smooth. Taste and adjust the flavour with more salt or lemon depending on your preferences. Store in the fridge until ready to use.
Heat the olive oil in a pan on medium heat. Season the salmon with the salt and pepper and then cook the salmon for 3 minutes per side until cooked through. Remove the salmon from the pan, place on a board and break into flakes using a fork.
Place the shredded lettuce in a bowl, top with the radishes, sliced avocado, cucumber, flaked salmon, pickled onion and toss with the dressing right before serving.