If baking your meatballs, preheat the oven to 400 F (204 C).
Finely dice your onion and thyme, if using fresh.
Mix together all ingredients EXCEPT the milk (ground meat, egg, thyme, oats, garlic powder, onion, flour, salt and pepper).
Add the milk, reserving a small amount (you may not need all of it) until you get a uniform consistency that holds together well. You can add the rest of the milk or more if you need it! Be careful not to overwork the ground meat, as it can affect the final texture. If the meat mixture is too wet, you can add some more flour to help it absorb some of the excess moisture.
You should have a uniform mixture that holds together when everything is incorporated.
Heat a pan over medium heat. Test cook a small amount of mix for seasoning, either in the pan or in the microwave for about 15 seconds. Add butter or vegetable oil to the pan and start to shape your meatballs using a tablespoon to create oval shaped meatballs (they can also be round, we've just always made ours longer than they are wide!) Add your meatballs to the pan as you make them and cook over medium to medium-low heat. Keeping the temperature on the lower side ensures that the meatballs do not burn.
Flip the meatballs once they have browned on one side. Make sure to rotate the meatballs out of the center if that's the hottest part of your pan!
Once your meatballs have cooked all the way through (no pink in the middle!), or reached an internal temperature of 165F (74C) take them out of the pan and repeat the process for any remaining mix you have left! You can also have two pans cooking at once.
If you're baking your meatballs, shape your meatballs and place on a prepared baking sheet. Bake for about 20-25 minutes until fully cooked through the center. Enjoy!