Toast the 2 slices of bread until golden and crisp, then place on a work surface.
Cut the ripe avocado in half, remove the pit, scoop out half of the avocado into a small bowl, and mash with a fork until creamy but slightly chunky.
Spread the mashed avocado evenly over each toast (use half the mashed avocado per slice).
Top each tartine with 2 tomato slices, 2 thin cucumber slices (or arrange cucumber evenly), and a portion of the smoked salmon (about 2 oz per tartine).
Scatter capers over the tartines, drizzle with olive oil, and squeeze fresh lemon juice over the top to taste.
Finish by sprinkling crushed red pepper flakes, flaky sea salt, and freshly ground black pepper, then serve immediately.
