Place onion slices in a bowl and toss with sugar and salt.

Next, add red onions to a jar and pour enough red wine vinegar so that the onions are half way submerged.

Next add water and cover the onion jar with its lid.

Shake vigorously and let sit for 1 hour but if you're in a rush, you could use them within 15 minutes.

After use, store onions in the fridge and use for up to 1-2 weeks.