Heat a large frying pan and add the sliced onion and diced jalapeño. Let the onion get golden on the edges; then add the butter and garlic. When the garlic is fragrant turn off the heat and set the mixture in a bowl.
Heat a large griddle and place the corn single layer. Dust with the ground cumin, dash of salt and pepper; when the corn slightly golden flip and do the same on the other side.
Place in a bowl; zest the lime and add the onion mixture and toss.
Juice the lime in a small bowl and add the balsamic vinegar, salt, pepper and stir.