Cut the cucumber into slices, quarter them, add salt & mix.
After about 5-10 min just squeeze the cucumber bits to drain the water - discard the water.
Chop the potatoes & the tomatoes & the spring onions & the arugula & the cress.
Mix everything.
Peel the avocado & discard the pit.
Add lemon juice & sour cream.
Mash everything & whip into a creamy dressing.
Add salt & pepper to taste.
Add dressing to potato salad & mix thoroughly.