Slice the cucumber into 1/4-inch thick rounds and halve the cherry tomatoes lengthwise—this exposes their seeds and allows them to absorb the dressing better. Pit and cube the avocado into bite-sized pieces. Thinly slice the fresh basil by stacking the leaves, rolling them tightly, and slicing across the roll (this technique, called chiffonade, prevents bruising the delicate herb). Finely mince the garlic. I like to add the garlic to the dressing rather than the salad itself, as it infuses the oil and vinegar with flavor more effectively than raw garlic scattered throughout.
In a small bowl, combine the extra virgin olive oil, balsamic vinegar, minced garlic, lemon juice, kosher salt, freshly cracked black pepper, and dried oregano. Whisk together vigorously for about 30 seconds until the mixture becomes slightly emulsified and the flavors begin to meld. I find that whisking the dressing separately before adding it to the salad ensures the garlic distributes evenly and the seasoning is perfectly balanced—you can taste and adjust if needed before it touches the delicate vegetables.
In a large bowl, gently combine the cucumber slices, halved tomatoes, fresh mozzarella pearls, cubed avocado, and sliced basil. Pour the dressing from Step 2 over the salad and toss gently with a large spoon or your hands, being careful not to crush the avocado or mozzarella. The key is to coat everything evenly without breaking down the delicate ingredients—think of it as folding rather than aggressively tossing.