Rinse the lettuce leaves (or mixed greens) thoroughly under cold running water to remove any grit. Shake off excess water and spin dry in a salad spinner or pat dry with clean kitchen towels or paper towels.

Chop lettuce

Stack the dry lettuce leaves and slice or tear them into bite-sized pieces. Place the chopped lettuce into a large salad bowl.

Prepare cucumber

Trim the ends of the cucumber. If the skin is waxed or you prefer, peel in alternating strips; otherwise leave the skin on for texture and nutrients. Cut the cucumber in half lengthwise, scoop out seeds if large and watery, then slice into 1/8–1/4 inch (3–6 mm) half-moons. Add to the bowl with lettuce.

Prepare carrot

Peel the carrot and remove the ends. Using a box grater, julienne peeler, or a sharp knife, shred or cut the carrot into thin matchsticks (julienne) or grate coarsely. Add the carrot to the bowl with the other vegetables.

Make dressing

In a small bowl or jar, combine the lemon juice, Dijon mustard, honey or maple syrup, salt, and black pepper. Whisk or shake to blend. Slowly drizzle in the olive oil while whisking (or add to jar and shake vigorously) until the dressing is emulsified and slightly thickened. Taste and adjust seasoning — add a little more lemon for acidity, salt for flavor, or honey for sweetness.

Assemble and serve

Pour about half of the dressing over the salad and toss gently with salad tongs or clean hands to coat the vegetables evenly. Taste and add more dressing as needed (reserve extra dressing for later).

If using, sprinkle the chopped parsley or dill and the toasted seeds or nuts over the top for garnish and extra texture.

Serve immediately so the greens remain crisp. Leftover dressing can be stored in a sealed container in the refrigerator for up to 5 days.