If making the pickled red onions, start with that to give them time to pickle.
Drain the tofu and use your hands to squeeze out as much water as possible. Crumble the tofu with your hands into bite-sized pieces into a large bowl. Sprinkle over the cornstarch and toss to coat the tofu.
Heat the oil in a large non-stick pan over medium-high heat. Add the tofu in a single layer, stir to coat in oil then leave to fry on the first side until golden brown. Stir and toss to fry on the other side until golden brown and crispy.
While the tofu fries, combine all the remaining ingredients for the tofu sauce in a small bowl.
When the tofu is fried, reduce the heat to low and pour in the sauce. Stir continuously while the sauce thickens and coats the tofu.
Make the sriracha mayo by combining the mayonnaise and sriracha in a bowl. Add a splash of water until the mixture can be drizzled - I added about a teaspoon of water.
Assemble the tofu lettuce wraps. Be careful not to overfill the cups, you want to be able to pick them up without losing all the filling! Arrange the lettuce leaves on a serving plate. Fill each with a spoonful of tofu crumbles and top with some carrot, pickled red onion, cilantro and peanuts. Drizzle each with some sriracha mayo.