Bring a large pot of generously salted water to a rolling boil. Add the tri-color rotini pasta and stir immediately. Cook for 8-10 minutes until al dente. Drain in a colander and briefly rinse under cold water to stop the cooking process.

In a small bowl, combine the red wine vinegar, Dijon mustard, minced garlic clove, dried oregano, salt, and pepper. Slowly drizzle in the extra virgin olive oil while whisking continuously until the mixture is fully emulsified and thickened.

Slice the cucumber into thin rounds or half-moons. Slice the cherry tomatoes in half and drain the black olives.

Transfer the cooled rotini to a large ceramic bowl. Add the halved cherry tomatoes, sliced cucumbers, and black olives. Pour the vinaigrette over the top and gently toss until completely coated. Fold in the crumbled feta cheese right before serving.