Slice the cucumber into 1/2-inch thick rounds and arrange them on a serving platter.
In a medium bowl, combine the cream cheese, dill, garlic powder, lemon juice, salt, and pepper. Mix until smooth and well combined.
Using a small spoon or piping bag, dollop or pipe the cream cheese mixture onto each cucumber slice.
Top each cucumber bite with a half cherry tomato, a sprinkle of red onion, and feta cheese if using.
Serve immediately or refrigerate for up to 30 minutes before serving for a chilled option.