Fill a medium saucepan with water and add the white vinegar, then bring it to a gentle simmer over medium heat.
In a small bowl, whip the ricotta cheese with the lemon zest and a pinch of the sea salt until the mixture is light and smooth.
Toast the slice of rye bread until it is golden brown and firm enough to support the toppings.
Crack each egg into a small ramekin, create a gentle whirlpool in the simmering water, and carefully drop the eggs in to poach for 3 minutes.
Spread the whipped lemon ricotta generously across the surface of the warm rye toast.
Layer the smoked salmon slices evenly over the ricotta base.
Use a slotted spoon to carefully remove the poached eggs from the water, pat them dry with a paper towel, and place them on top of the salmon.
Garnish the dish with the remaining sea salt, black pepper, and fresh chives before serving immediately.