MAybe spray some non-stick cooking spray and move the onions around constantly. If the green onion stays in one place of course its going to get burned.
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try spraying some pam on some foil, seal the foil then cook with the onions in the foil. along with a little water, not directly on the heat
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You may need to soak them in water overnight, so they absorb as much water as possible. You may also want to spray them with water while they are cooking to keep the green from getting overheated.
The other thing is how hot is your grill? The green onions may have to be grilled at a less intense heat than full hot coals- or can you put them on a higher rack?
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I had the same issue and i was told to boill them until soft and then grill them..Works a treat..!!
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indirect heat.
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