In a medium bowl, toss together the cucumber and red onion. Set aside.
In a small bowl, whisk together the remaining ingredients. Pour over the cucumber and onion. Toss to combine.
Cover and refrigerate at least one hour prior to serving.
I used dill paste (look for it in the supermarket next to fresh herbs) because it's a pandemic and fresh dill is super perishable. It's basically squeezable fresh dill in a bit of oil. Using fresh dill would be great too!