Trim the green onions to fit in your canning jars. You'll want the tops of the onions to come just 1/2" under the lip of the jar. Pack them tightly, but do not overpack.
To each jar, add one clove of smashed garlic, 2 tsp pickling spice (for 1 Tbsp total - divided), and dill.
In a small saucepan, combine the vinegar, water, sugar, and salt and heat just until the sugar and salt are dissolved. Push off the heat and allow to cool.
Once the brine is cool, pour over the top of the onions in each jar. Discard any remaining brine (or use for more if you wish).
If using crushed red pepper, add to the top at this time. Place the canning lid and ring on each jar and screw finger tip tight.
Place jars in refrigerator and allow one day for the flavors to come together before enjoying. Use within 7 days.