In a medium bowl, whisk together the vinegar, orange juice, sugar and salt. Add in the carrots, radishes and cucumber, and toss to combine. Let the mixture sit while you prepare the rest of the recipe, tossing once or twice.
For the mushrooms:
In a large bowl, whisk together 1 tablespoon of the olive oil, the soy sauce, lime juice, garlic, maple syrup and red pepper flakes. Add in the sliced mushrooms and toss until well combined. Let the mushrooms marinate for 30 minutes at room temperature, tossing once halfway through.
Add the remaining 1 tablespoon olive oil to a large nonstick skillet set over medium high heat. When hot, add in the mushrooms (shake off any excess marinade first) and the onion. Cook for about 8 to 10 minutes, until tender and the juices have cooked off.
In a small bowl, mix together the mayo and sriracha.
To assemble, add some of the brown rice to a bowl. Top with some of the cooked mushroom mixture, the pickled veggies (using a slotted spoon to drain and discard the juices), the red cabbage, cilantro and peanuts. Drizzle with the sriracha mayo.