Make the dressing: In a large serving bowl, whisk together the 3 tablespoons fresh lemon juice, 1 garlic clove, 1 teaspoon dried oregano, and salt and freshly ground black pepper. Whisk in the ⅓ cup extra-virgin olive oiltaste and add more salt, pepper or lemon juice as needed. Set aside.
Prepare the pasta: Bring a large pot of heavily salted water to a boil. Cook the 1 box gluten-free pasta according to the package directions to al dente (still slightly firm). Drain, transfer to the large bowl, and toss with the dressing while still warm.
Pile in the sliced 3 large tomatoes, 8 ounces fresh mozzarella, ½ cup thinly sliced cucumber, and 3 tablespoons diced red onion. Toss well, then fold in 1 cup coarsely chopped fresh basil leaves. Taste and season with more salt if needed.
Drizzle with olive oil and top with cracked black pepper just before serving.
Notes
Don't overcook the pasta. "Al dente" means just slightly firm. This can be tricky with gluten-free pasta because you don't want to undercook it, but overcooking it can lead to mushy pasta salad. So, pull it off the stove when the pasta has some give but isn't soft. It will soften up more in the dressing.
Toss the pasta when warm. Drain the pasta well, then immediately add it to the bowl with the dressing. The warm pasta will soak up the delicious lemony dressing, making it super flavorful.
Make it ahead - but not too far ahead. You can definitely make this salad earlier in the day you wish to serve it, but I don't reccomend making it too far in advance because the pasta will soak up the dressing and can become overly firm in the fridge.
Leave at room temperature. I like to make the dressing and toss it with the warm pasta a few hours before I plan to serve it, and then add in the vegetables, herbs and cheese just before serving so that everything stays fresh.
Serve warm or cold. Depending on your preference, you can serve your pasta salad warm, room temperature, or chilled in the fridge. Again, you don't want to let it stay in the fridge long enough for the pasta to get hard, but about an hour will cool it to that classic pasta salad presentation. Personally, I prefer this salad warm or room temperature; you do you!