Make the sauce: in a small bowl or measuring cup, whisk together the peanut butter, liquid aminos (or coconut aminos), red curry paste, and fish sauce (if using) until smooth; set aside.
Heat the oil: warm 1 tablespoon avocado oil in a large 12-inch skillet or sauté pan over medium-high heat.
Sauté the onion: add the finely chopped red onion and cook, stirring occasionally, until it begins to soften, about 3 minutes.
Brown the turkey: push the onion to the sides of the pan and add the ground turkey to the center; let it brown undisturbed about 2 minutes per side, then break it up with a spatula into bite-sized pieces.
Add vegetables: stir the grated carrots and thinly sliced red cabbage into the turkey until combined.
Combine with sauce: pour the prepared sauce into the skillet and stir continuously until the sauce thickens and the vegetables reach your desired tenderness, about 2–4 minutes.
Finish: stir in the chopped green onions and cashews if using, then remove from heat.
Assemble: wash and dry butter leaf lettuce, place leaves on a plate, spoon the Thai turkey mixture into each leaf, and serve.
