Toss the diced kohlrabi with olive oil, garlic, and salt. Add some coarsely chopped onion pieces if you like, half way thru roasting. Roast in a roasting pan (not a cookie sheet, needs sides) so that you may toss them over every now and then. You want to cook them until the bottom starts to stick then toss and repeat. It will take about 45 minutes to cook.