Step 1

Preheat oven to 350°. Cut cucumbers about 1" thick on a steep diagonal and place in a medium bowl. Add a large pinch of kosher salt and 2 tsp. vinegar and toss to combine; let marinate 10 minutes. Pour off any liquid that is released.

Step 2

Toast ¼ cup almonds on a rimmed baking sheet, tossing once, until golden, about 5 minutes. Let cool, then coarsely chop. Set aside.

Step 3

Blend garlic, oil, remaining 1 tsp. vinegar, remaining ½ cup almonds, and ½ cup ice water in a blender until smooth and creamy, about 2 minutes; season generously with salt.

Step 4

Divide sauce among plates and top with cucumber salad and chopped almonds. Sprinkle with flaky sea salt.

Step 5

Do Ahead: Sauce can be made 1 day ahead. Cover and chill.