Combine sour cream, milk, zest and a pinch of salt and a few grinds of fresh pepper in a small bowl and mix until it is all incorporated.
Add the roe, cucumber and red onion. Stir to combine. Let the salad sit for 15 minutes taste and adjust the seasoning. Divide it between 4 small bowls, add a few sliced scallions and a grind of fresh ground black pepper. Serve.