Cut the cabbage in half. Cut away the hard core and slice the cabbage crosswise into 1/2-inch strips, then crosswise into 3/4-inch pieces. There should be 4 cups; if there is extra, set it aside to add to soup or another salad. Place the cabbage in a mixing bowl.
Add the tomatoes, parsley and scallions, and toss with a fork to combine.
In a small bowl, whisk the lemon juice, garlic and salt until the salt dissolves. Mix in the oil.
Season the dressing to taste with pepper. Pour the dressing over the salad, toss for 1 minute to coat it well, then let sit 10 minutes for flavors to meld. Serve immediately.