Place the diced steak in a large resealable plastic bag. Add the garlic and onion powders and a big pinch of salt. Seal the bag and toss the meat with the spices. Marinate in the fridge for at least 2 hours. Overnight is fine, too.
Meanwhile, cook the farro according to the package instructions.
In the meantime, set your oven to broil. Place the frozen corn on one half of a large baking sheet and the onion slices on the other. Drizzle with two teaspoons of oil and a good pinch of salt. Broil, checking and stirring in 5-minute increments, until the corn is charred and popping around on the baking sheet and the onion is also charred and tender, roughly 15 minutes.
Heat a large skillet over medium-high heat, then add the marinated meat straight from the bag. Cook the meat in the skillet, until browned all over and cooked through, about 5 minutes.
Make the guacamole by mashing the avocado with a tablespoon of fresh lime juice and the cilantro. Season with a pinch of salt.
Start building your bowls! Add about half a cup (a little more perhaps) of cooked farro to each bowl, followed by a helping of seared meat, the charred corn and onion, a dollop of guacamole and a little spooning of salsa. Garnish with shredded Cheddar, lime wedges and a sprig or two of cilantro.
I like to cook a bunch of farro at the beginning of the week and make different grain bowls all week long.