Add the diced cucumber, halved tomatoes, bell pepper, sliced onion, olives, and crumbled feta to a large mixing bowl, arranging them evenly so each ingredient is well distributed.
In a separate bowl, combine the red wine vinegar, lemon juice, Dijon mustard, minced garlic, oregano, salt, and pepper, whisking until the mixture is smooth and well blended.
Slowly pour in the olive oil while whisking continuously, allowing the dressing to emulsify and become slightly thickened and cohesive.
Drizzle the prepared dressing evenly over the salad, making sure it reaches all the ingredients without soaking any one area too heavily.
Gently toss the salad until everything is lightly coated, being careful not to break up the vegetables or feta too much.
Taste and adjust seasoning with additional salt and pepper if needed, keeping in mind the natural saltiness of the feta and olives.
Serve immediately for the freshest texture, or chill briefly before serving if you prefer it slightly cold.
