Combine vinegar, sugar and water in a pot on the stove. Bring to a boil, turn down heat and allow to simmer for 10 minutes. It will thicken somewhat.
Add garlic, salt and chili (flakes or fresh). Remove from heat and allow to cool 10 minutes.
Cut cucumbers in half, lengthwise. Remove seeds. Slice lengthwise into halves and then quarters. Cut each strip in half so that each piece is about 3-4 inches in length.
Place cucumbers in a shallow glass or plastic container. Pour prepared vinegar syrup over top, including chili and garlic cloves. Stir gently so all the cucumbers are coated. Seal container with a lid or plastic wrap. Add green onions. Store in fridge for 4 hours before serving. Will keep in fridge up to a week.