Bring a large pot of salted water to a rolling boil—you want it as salty as seawater. Drop in your rotini and cook according to package directions until just tender but still with a slight bite. I learned this the hard way: overcooking pasta by even two minutes turns your cozy cold pasta salad summer mushy and sad. When it's done, drain immediately but don't rinse (the starch helps the dressing cling).
While the pasta drains, whisk together olive oil, lemon juice, dried oregano, salt, and black pepper in a small bowl. The dressing should smell bright and herbaceous, not muted. This is my secret moment: I always taste it on my fingertip before moving forward. If it needs more punch, add another squeeze of lemon juice—you can't adjust this later once everything's mixed.
Pour the warm dressing over the still-hot pasta and toss vigorously for about one minute. This is non-negotiable, because the heat opens the pasta's surface and lets the flavors sink in rather than sitting on top. I confess I used to skip this step and wondered why my salad tasted flat. Now I set a timer to make sure I'm actually tossing for the full 60 seconds.
Add the diced mozzarella cheese while the pasta is still warm—this prevents the cheese from clumping or getting rubbery later. Stir gently but thoroughly, letting the warmth soften the edges just slightly. You're aiming for pockets of cheese throughout, not melted strings. Watch how the texture changes as you fold it in; this is the moment your cozy cold pasta salad summer recipe transforms from basic to special.
Add the halved cherry tomatoes, diced cucumber, finely chopped red onion, sliced chicken breast, and sliced olives. Fold everything together with a rubber spatula using gentle, deliberate motions—you want distinct pieces, not crushed vegetables. This takes about two minutes, and yes, it matters. I've rush-folded before and ended up with broken tomatoes and soggy salad.
Transfer to a serving bowl and refrigerate for at least 30 minutes before serving. This resting time lets the flavors deepen and marry together. The texture transforms as the pasta cools—it firms up, and the dressing fully distributes. If you're meal prepping, you can refrigerate for up to three days in an airtight container.