Place cream cheese, Feta, half & half, mint, and garlic powder in a large mixing bowl and season with salt and black pepper, to taste.
Beat with a hand mixer or immersion blender until mixture is light and fluffy. Set aside.
Trim the base of each cucumber slice so that it sits flat. Carefully scoop out the interior of each cucumber slice with a small measuring spoon or melon baller, leaving enough space on the bottom and sides to form a small “cup.” Do not scoop all the way through!
Transfer some of the whipped Feta mixture to a pastry bag fitted with a large star or round tip (or use a plastic sandwich bag with one of the bottom corners removed).
Carefully pipe the whipped Feta into each cucumber cup and set on a serving platter.
Serve immediately garnished with sprigs of mint, if using.
Notes
A medium-size cucumber will yield about 4-5 cucumber cups, an English cucumber will yield about 8-10 cucumber cups.
Cucumbers can be peeled, partially peeled, or unpeeled depending on personal preference.