Mama's Slaw

In a large bowl, combine the cabbage, onions, tomatoes, mayonnaise, salt, and pepper. Toss thoroughly. (You can prepare this up to 6 hours in advance and store it, covered, in the refrigerator. But if you do, do not add the salt until you’re ready to serve the slaw, and toss it again just before serving; otherwise, the slaw becomes watery.)

Serve immediately.