Arrange the watermelon chunks on a large serving platter, ensuring an even distribution of color and size for visual appeal.
Use a sharp chef's knife to peel, pit, and thinly slice the avocado into even slices. Gently fan out the avocado slices over the watermelon on the platter.
Sprinkle lemon juice evenly over the fruit to prevent browning and add brightness. Lightly season with salt and pepper to taste.
Gently toss the fruits in the bowl to distribute the lemon juice and seasoning without breaking the avocado slices, then transfer the mixture back onto the platter if needed.
Finish by arranging the salad attractively on serving plates, optionally garnishing with additional herbs or a drizzle of olive oil for extra flavor.