Combine olive oil, fresh lemon juice, lemon zest, salt, and black pepper in a small bowl or mason jar. Whisk or shake until fully emulsified. Taste and adjust seasoning to ensure the dressing is bright but balanced.
In a large bowl, gently mix diced avocado, mango chunks, cherry tomatoes, red onion, and basil leaves. Be careful while tossing to avoid bruising the avocado.
Drizzle the vinaigrette over the salad and toss lightly to coat everything evenly. Serve immediately for the freshest flavor, or chill for 15–30 minutes to allow the flavors to meld.