Make dressing: Mix oil, vinegar, dried herbs, salt, black pepper, and red pepper in a large bowl with a tight-fitting lid.
Add cucumbers, tomatoes, and onions: Add the vegetables, and toss well to coat and combine.
Marinate: Leave at room temperature for one hour. Toss again, and taste for salt and pepper. Adjust seasoning as needed. Cover with lid (or spoon into a zip-top bag), and store in the fridge for 12 to 24 hours, stirring occasionally.
Season and serve: Let come to room temperature for 30 to 60 minutes before serving. Top with optional minced herbs.
