Step 1: Cook the tortellini according to package directions until al dente. Drain thoroughly and immediately rinse with cold water to stop the cooking process and prevent sticking. Set aside to cool completely.
Step 2: While the tortellini cools, prepare your vegetables. Halve the cherry or grape tomatoes, dice the English cucumber, and finely chop the red onion and bell pepper. If you're using fresh mozzarella pearls, drain them.
Step 3: In a small bowl, whisk together the extra virgin olive oil, red wine vinegar, Dijon mustard, minced garlic, dried oregano, salt, and black pepper. Taste and adjust seasonings as needed.
Step 4: In a large mixing bowl, combine the cooled tortellini, halved tomatoes, diced cucumber, chopped red onion, bell pepper, and fresh mozzarella pearls (if using).
Step 5: Pour the prepared dressing over the tortellini and vegetables. Toss gently to ensure all ingredients are well coated. Add the crumbled feta cheese and fresh basil, then toss once more.
Step 6: Cover the bowl and refrigerate for at least 30 minutes to allow the flavors to meld. For best results, chill for 1-2 hours. Before serving, give it another gentle toss.