Most chopped salads are built on a base of lettuce; I prefer softer greens here, but you can certainly use romaine or cabbage. To complement the lettuce base, I add diced ripe tomatoes, which are abundant at just about any farmers market right now. Cucumbers or radishes would be equally good.
Diced ham is my protein preference, but any other deli meat will work — simply ask for 1/4-inch thick slices at the grocery store and cut into cubes when you get home. Drained and rinsed canned beans make a good vegetarian option; even better is a half-dozen hard-cooked eggs. Most grocery stores sell them precooked these days, but you can make them yourself, within the 30-minute time frame, if you start the eggs before you do anything else. Steaming, my favorite method for preparing hard-boiled eggs, is written in the recipe below.