Cook the buckwheat according to package instructions. Usually, this involves boiling it in water until tender, about 15-20 minutes. Drain and set aside to cool slightly.

While the buckwheat cooks, hard boil the eggs. Place eggs in a pot, cover with cold water, bring to a boil, then remove from heat, cover, and let stand for 10-12 minutes. Drain, cool under cold water, peel, and quarter.

In a small bowl, whisk together the lemon juice and olive oil. Season with salt and pepper. If using the optional sour cream, whisk it into the dressing now for a creamier texture.

In a large bowl, combine the lettuce leaves, cucumber slices, cooled buckwheat, and drained tuna.

Gently toss the salad with the prepared dressing until everything is lightly coated.

Divide the salad among plates. Arrange the quartered hard-boiled eggs on top.

If using the optional cheese, sprinkle it over the salad.

Serve immediately and enjoy your healthy, satisfying lunch!