Make the marinade by whisking chopped lemongrass, grated ginger, honey, 2 tablespoons soy sauce, fish sauce and minced garlic together in a bowl; add the sliced skirt steak, seal in a zip-top bag or cover bowl, and refrigerate for 20–30 minutes or overnight.
Cook the spaghetti squash: pierce it several times with a sharp knife and microwave whole on high about 15 minutes, turning every 5 minutes, until just tender; let cool slightly, then halve lengthwise and scrape the strands with a fork.
Heat a large skillet over medium-high and add a drizzle of peanut or sesame oil; sauté chopped bok choy and sliced mushrooms about 8–10 minutes until bok choy wilts and mushrooms caramelize, season with salt and pepper, then transfer to a plate and cover to keep warm.
Return the skillet to high heat with another drizzle of oil; add the marinated steak in a single layer and sear 2–3 minutes, toss and cook another 2–3 minutes until cooked through; pour any remaining marinade into the pan and cook 1 minute more, then remove and keep warm with the vegetables.
Make the peanut sauce by combining the coconut milk, peanut butter, brown sugar, 2 tablespoons soy sauce and Thai red curry paste in a medium saucepan; warm over medium heat, stirring until smooth and just simmering.
Assemble bowls by dividing spaghetti squash among bowls, topping with bok choy, mushrooms and sliced beef, then drizzle with peanut sauce and finish with desired garnishes (chopped peanuts, sliced chilies, shredded carrots, mint, Thai basil, or chopped lemongrass).
