Peel the potatoes and carrots, then dice them into even, bite-sized chunks so they cook through at the same rate.

Trim the ends off the green beans and chop them into short, half-inch pieces.

Bring a saucepan of salted water to a boil, add the potato, carrot, green beans, and peas, and cook until the potato and carrot are fork-tender but not mushy.

Drain the boiled vegetables in a colander and let them cool to room temperature before adding the raw ingredients.

While the boiled vegetables cool, dice the cucumber and finely chop the onion.

In a small bowl, whisk together the lemon juice, black pepper, salt, and olive oil until the dressing is smooth and slightly emulsified.

Combine the cooled boiled vegetables with the diced cucumber and onion in a large mixing bowl.

Pour the dressing over the vegetables and toss gently so everything is evenly coated without mashing the potato.

Let the salad rest so the vegetables absorb the dressing, then taste and adjust the salt or lemon before serving.