Divide cucumbers amongst 4 wide mouth 1 qt mason jars. Add 1 tsp mustard seeds, 1 T dried onion and one minced or pressed garlic clove to each jar.
Add water, vinegar, salt and sugar to a large saucepan on the stove; bring to a boil. Stir occasionally until salt and sugar are dissolved. Pour brine into jars. Cap tightly and leave out on the counter top for 2 days.
On day 2, flip the jars upside down.
Transfer to fridge on day 3.