Remove the tofu from the package and press to remove excess fluid. See note on pressing tofu.
While the tofu is pressing, place the chopped onion, garlic and one tablespoon olive oil together in a medium-size container.
In a small bowl, whisk together the miso, tamari, and vinegar. Add this to the chopped onion mixture and stir until well-combined.
Chop the tofu into 1/2" cubes and place in the pan with the miso marinade. Stir everything together gently so that the marinade permeates the tofu. Let the tofu marinade for at least 30 minutes or up to an hour.
Pour remaining oil in skillet over medium to medium-high heat. Let the oil heat up for about a minute. Use tongs to carefully place tofu pieces in the skillet and slightly brown each side of the tofu cubes. Continue cooking and tossing the tofu until the tofu is slightly browned. Then turn heat to low and add the remaining marinade. Cook for a minute or two until the onions are tender.
Store cooked tofu in an airtight container in the fridge for up to 5 days. Tofu changes its consistency when frozen so it's not recommended to freeze this recipe.
To serve, place tofu pieces over rice, cauliflower rice, in vegetable wraps, salads, etc. To reheat, cook in a skillet, air fryer until, or microwave until heated through.