Cut open the avocado and scoop the flesh into a bowl, discarding the pit. Add the lemon juice, sea salt, and black pepper. Use a fork to mash the ingredients to desired consistency.
Spread the mashed avocado evenly onto toasted bread slices. Top with fresh mozzarella slices, tomatoes, and basil. Season with additional salt and pepper, if desired. Drizzle with balsamic glaze and serve immediately.