Set Ninja Cooker on low, spray pan, turn it on the slow cooker low setting.
Add ground beef to pan, use the Mix 'n Chop to grind up the meat.
On a small cutting board, slice and chop your onion into small pieces, add to the meat.
Season well. Season generously. Remember we're adding a ton more ingredients and there's an opportunity to season it later, too. But go ahead and add all your seasonings in at this time.
Using the Mix 'n Chop again, ensure the mixture is well-blended before moving on to the next step.
Add your Worcestershire and minced garlic to the pan, mix with a wooden spoon until well blended.
Add in all your ketchup, tomato paste, and brown sugar to the pan.
Mix with wooden spoon until thoroughly and completely covered and well-blended.
Place lid on the slow cooker, and set timer for 4 hours and let it cook for 3 hours untouched.
During the fourth hour, you can opt to taste the sauce to add any additional seasonings needed. You don't have to add seasoning here, but it's important to stir.
Continue to let cook for the next 50 minutes.
Turn off the Ninja Cooker (or turn it to buffet) and remove the lid, but stir to ensure everything is well mixed and to let it slightly cool at this time, let the sauce slightly thicken up. Taste and add to adjust any seasonings if desired.
Stir your final seasonings into the Slow Cooker Sloppy Joes, mixing well.
Turn off the slow cooker if you’re ready to serve. Let it cool a tad before serving.
Before serving, if you'd like to "up" your sloppy joes game, lightly butter both sides of the buns and toast on a hot griddle or in a large skillet over medium high heat. Gently buttering and toasting the bun helps it withstand the weight/sauce of the sloppy joes AND it tastes AMAAAAAZING!
Carefully spoon or ladle beef mixture onto burger buns to serve. Serve with pickles, chips, or whatever side you like!