In a small bowl, stir together the hoisin, liquid aminos, apple cider vinegar and olive oil and set aside.
Press the tofu with paper towels to squeeze out as much liquid as possible.
Heat grape seed oil in a large non-stick skillet over med-high heat. When the oil is hot, crumble the tofu into small pieces into the skillet and turn frequently with a spatula as it cooks for about 5 minutes.
Stir in mushrooms and continue to cook, stirring frequently, for 3 minutes or until remaining tofu liquid is cooked off.
Add celery, garlic, ginger, red pepper flakes, and half the green onions. Combine ingredients evenly and continue to cook for 2-3 minutes stirring frequently.
Pour the hoisin mixture over the top of the mushroom/tofu mixture and toss to coat. Cook an additional 2 minutes, stirring frequently. Then remove from heat.
Spoon mixture into lettuce leaves (cups), top with remaining green onions and additional pepper flakes if desired. Enjoy!