Bring a large pot of generously salted water to a rolling boil. Add the pasta and cook until al dente, according to package directions. Drain and rinse under cold water until completely cool; shake off excess water.

While the pasta cooks, halve the cherry tomatoes, dice the bell pepper, thinly slice the red onion, halve the olives, cut the salami into thin strips, and drain the mozzarella pearls.

In a small bowl or a jar with a lid, combine the olive oil, red wine vinegar, Dijon mustard, minced garlic, oregano, salt, pepper, and red pepper flakes if using. Whisk or shake until emulsified.

In a very large bowl, combine the cooled pasta, salami, mozzarella, tomatoes, olives, bell pepper, and red onion. Drizzle the dressing over the top and toss gently but thoroughly to coat everything.

Cover and refrigerate for at least 30 minutes, preferably 2 hours, to let flavors meld. Before serving, toss again, add the torn basil, and adjust salt and pepper. Garnish with extra basil leaves and a drizzle of olive oil.