Slice onions in half (keep tip intact so it does not come apart), rub with oil and place on a hot 400°F grill until tender and lightly charred, about 3-5 minutes.

Carefully slice ¼” off root end so it can stand up straight, and place in a baking dish. Spread on about 1Tbsp of the nut butter onto each onion half. Broil until butter is melted and serve hot.