Prepare the Vegetables: Slice cucumbers, tomatoes, and onions. Place in a large bowl or jar.
Make the Marinade: In a separate bowl, mix vinegar, water, sugar, salt, and pepper. Add olive oil, garlic powder, oregano/dill, and red pepper flakes if using. Whisk to combine.
Combine: Pour the marinade over the vegetables, making sure they are fully submerged. Toss gently to coat evenly.
Marinate: Cover and refrigerate for at least 1 hour, but preferably several hours or overnight, to allow the flavors to meld.
Serve: Enjoy as a side dish with grilled meats, fried foods, or as a refreshing salad.
