This is a very simple green salad my mom used to put on the table every night. She was able to get kids who never ate their vegetables to love this salad. I think the secret is in the vinaigrette: it's got the perfect level of acidity to balance out all the greens.
For the salad: In a large bowl, add the lettuce, celery, and tomato. Thinly slice the cabbage. Cut the carrots in half lengthwise, then slice. Shave the radishes on a mandoline. Thinly slice the green tops of the onions. Add everything to the bowl and refrigerate while making the vinaigrette.
For the vinaigrette: In a jar with a tight-fitting lid, add olive oil, vinegar, ½ teaspoon salt, pepper, and lemon juice. Cover and shake. Spoon vinaigrette from the bottom of the jar onto a piece of lettuce and taste.
Assemble the salad: Season the chilled greens with ¼ teaspoon salt and a few grinds of pepper. Give the dressing a stir and then drizzle around the outer edge of the bowl. Gently toss with your hands to combine. Taste one more time, adjust seasoning, and serve.