Season the brisket with the pepper, garlic, onion powder and paprika.
Cover the bottom of a large Pyrex dish with the onions.
Mix the keto ketchup, 3/4 cup water, tomatoes and add a tablespoon of onion powder, mix well and set aside.
Put the brisket in a dish and pour the keto ketchup, 3/4 cup water, tomatoes and onion powder mix on top.
Add enough water to cover the brisket and cover the top of the dish.
Microwave on high for 25 mins, then remove the dish from the microwave and flip the brisket.
Repeat this proces again and add more of the sauce mix if you would like for more of that flavor.
Take the brisket out, let it cool and then slice.