Add Greek yogurt, cream cheese, lemon juice, dill, olive oil, and salt (if using) to a food processor.
Blend until very smooth and mousse-like, adding cold water one teaspoon at a time until light and spoonable.
Spoon into a ramekin and serve warm with a little extra dill or lemon zest. If serving with bell peppers, halve the mini bell peppers lengthwise, remove seeds, and steam briefly. Scoop the mousse into the peppers and chill before serving.
Notes
Make sure all bones and skin are removed from the salmon before blending.Taste before adding salt, as salmon and cream cheese can already be salty.Chill briefly for a firmer texture when serving in bell peppers.