You likely already know how to chop vegetables, but preparing them to thread onto kabob skewers requires a little extra attention to detail. You want the peppers and onions on your kabobs to finish cooking about the same time as the meat and any other ingredients, and you don't want layers of onion falling from the skewers into the grill. Cut peppers and onions into pieces about the same size, but use a different technique for each vegetable.
Stand a bell pepper upright and slice the outer walls of the pepper off of the stem and seeds. Discard the stem and seeds.
Lay the bell pepper walls flat and cut them into pieces roughly 1 to 1 1/2 inches square -- about the same size as the meat on the kabobs, if you are using meat.
Slice an onion in half lengthwise. Lay the onion halves on the cutting board cut sides down and chop off each end. Peel the skin from the onion halves and discard the skin and ends.
Chop each onion half lengthwise into four wedges. Cut the wedges in half crosswise if the onion is large; the onion pieces should be approximately the same size as the pepper pieces.
The kabob skewer should go through each layer when threading an onion wedge.