Make the salad dressing by mixing the lemon juice, olive oil, lemon zest (if using it), a pinch of salt, and a pinch of pepper until combined. Finely dice the red onion and add it to the dressing to soften a bit.
Prepare the remaining salad ingredients. Halve the baby tomatoes. Deseed and chop the sweet pepper (or bell pepper). Halve the avocado, remove the seed, and then peel it (or gently scoop up the whole half of the avocado using the spoon). Cut the avocado into cubes. Finely slice the fresh basil by placing the leaves on top of each other, rolling them, and then finely slicing them. Add the drained mini mozzarella pearls.
Toss the salad ingredients gently with the dressing until evenly coated. Taste and adjust the seasoning if needed, adding more salt or pepper to taste. Serve immediately.
