Place the cucumber slices, cherry tomatoes, red onion, and cilantro in a large bowl.
Sprinkle the vegetables with kosher salt, black pepper, garlic granules, and dried oregano.
Drizzle the salad with olive oil and lemon juice. Gently toss to combine.
Serve immediately, or let rest at room temperature for 10 minutes to allow the flavors to meld. Gently toss again before serving.
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Notes
Don't skimp on the olive oil! It's what makes the salad so flavorful. I've seen recipes that add 1 or 2 tablespoons of it. I highly recommend using the full three tablespoons. It will make a big difference.
Definitely use good olive oil in this recipe. Pick extra-virgin olive oil packaged in a dark glass bottle, and read the ingredients list to make sure it's pure olive oil and wasn't mixed with another oil.
Make sure to slice the onions very thinly. No one wants to bite into a big chunk of sharp onion in their salad.
When you sprinkle the spices over the salad, it might seem like a lot, but I recommend using all of them. They make the salad very flavorful.
This is not a good recipe to make ahead of time. It's best enjoyed when freshly assembled or after a short rest to allow the flavors to meld. But if you find yourself with leftovers, they'll keep alright in the fridge, in an airtight container, until the next day. I wouldn't try to keep them beyond that.