Soak 12 bamboo skewers in a pan of water while preparing vegetables. This helps to prevent the skewers from burning during the grilling process.
Prepare yams by peeling and slicing them into 3/4-inch thick rounds. In a microwave safe bowl, cook the potatoes for 90 seconds. Mix and cook another 90 seconds. Set aside.
Slice zucchini into 3/4-inch thick rounds. Chop bell peppers and red onions into large, 2 inch pieces.
Combine all vegetables in a large mixing bowl and drizzle with olive oil and salt. Mix just until vegetables are coated.
Stack vegetables onto skewers. Be sure to leave just a sliver of space between each vegetable so that the heat will be able to cook between them.
Heat an outdoor grill to 450 degrees. Grill the kabobs by turning each skewer with tongs 4 times, cooking for 3 minutes between turns. The potatoes should be soft but not mushy. The zucchini, onions and peppers, should be crisp-tender. Sprinkle with additional seasoned salt if desired. Serve immediately.