Salmon and Mushroom Ceviche

This is my Dad's recipe...something we all enjoyed at summer BBQs.  You have to love seafood cooked in citrus to truly enjoy this. Super simple with few ingredients, but oh so good!!  This makes 4 appetizer servings.

1 pound boneless, skinless salmon, preferably center cut, cut in thin slices on the diagonal
1  1/2 lemons
sea salt
white pepper
12 medium white button mushrooms ( or more if you like - just increase the olive oil a bit)
4 Tbl olive oil
1 Tbl minced fresh dill
dill sprigs for garnish (optional)
thin slices of preserved lemon for garnish ( optional )
4 small salad plates

Toss the thinly sliced salmon gently with the juice of one lemon and a light dusting of sea salt and white pepper.  Cover and refrigerate for 30 minutes.
After 30 minutes, thinly slice the mushrooms and toss with the juice of the half lemon, the olive oil and a little more sea salt and white pepper.
Arrange equal portions of mushrooms and salmon on each of the four plates.
Sprinkle the salmon with the minced dill, garnish and serve immediately.