Chop mushrooms super fine or blend in a food processor. In a larger bowl, combine ground beef and mushrooms and kneed until mixed well.
Turn Instant Pot onto saute and wait until it is hot to add meat. Cook meat until no longer pink then drain off excess fat and water. Turn Instant Pot off.
Return meat to pot then add brown rice and broth on top. Don't stir. Add taco seasoning to the top and use a spoon to lightly move it around. Do not disturb the rice below.
Close Instant Pot and set to sealing position. Select manual high pressure (the manual button or the pressure cook button on the newer models) and set timer for 22 minutes. When timer is up allow for a full natural release (this takes about 12-15 minutes).
Give everything a good stir then move the rice mixture to the side. Add black beans to the empty space and close up the pot. Let it sit for 5 minutes to warm the beans. Do not set it for any cook setting because you will burn the rice and beans!
Once beans are warmed give everything another good stir and serve! Top with all of your favorite toppings.