In your blender combine celery, onion, carrots, green onion, spinach, garlic, and beef broth. Puree until liquid.
In the skillet you cooked your beef in, pour the green sauce over the meat and cook on medium, stirring frequently, until all water has evaporated and beef is absorbing the green sauce. This is how you have so many hidden vegetables in your chili! (yes, it looks a little weird to have “green meat” in the skillet, but once it is in the chili it is not green anymore!)
Once the meat has absorbed most of the green sauce, place it in your crockpot. You can alternatively cook this in a large dutch oven or stockpot on the stove, but it will need to be watched a little more closely than if you used a slow cooker. Simmer your chili on low for 2-3 hours on the stovetop. Stir every now and then to make sure it's not sticking to the bottom of the pan.
If using a slower cooker, add all remaining ingredients and cook on low for 6 hours or high for 3 hours. If you cook on high make sure to stir frequently to avoid burnt and stuck layers on the bottom and edges. I prefer to really slow cook it so the flavors have more time to mix together and get deep into the meat.
Cool and store any leftovers in the fridge for 5 days. Or you can freeze it in a freezer-safe airtight container for up to three months.