Remove the crusts from all bread slices. Set aside.
Peel the cucumber in alternating stripes, then slice into 1/8-inch thin rounds using a mandolin or sharp knife.
Lay cucumber slices on paper towels, sprinkle with coarse salt, and let rest 15–30 minutes to draw out moisture. Pat completely dry.
In a medium bowl, beat together the cream cheese, mayonnaise, fresh dill, fresh chives, lemon juice, garlic powder, and salt with a handheld mixer until smooth and fluffy.
Spread the herbed cream cheese generously on one side of all 16 bread slices.
Layer cucumber slices over 8 of the bread slices. Season with cracked black pepper.
Top with the remaining 8 bread slices, cream cheese side down. Press gently.
Using a sharp chef’s knife (wiping clean between cuts), cut each sandwich into quarters. You’ll have 32 tea sandwiches.
Serve immediately and enjoy!