Whisk together 2 tablespoons chopped lemongrass, 2 tablespoons grated ginger, 2 tablespoons honey, 2 tablespoons soy sauce, 1 tablespoon fish sauce, and 2 minced garlic cloves in a bowl.
Place the sliced skirt steak in a resealable bag or bowl and pour the marinade over it; seal and marinate 20–30 minutes at room temperature or refrigerate overnight.
Cook the spaghetti squash: pierce it several times with a sharp knife and microwave on high about 15 minutes until tender, turning every 5 minutes; let cool slightly, then halve lengthwise and scrape strands with a fork.
Heat a large skillet over medium-high and add a drizzle of 1–2 tablespoons peanut or sesame oil. Add the chopped bok choy and sliced mushrooms and sauté about 8–10 minutes until bok choy wilts and mushrooms caramelize; season with salt and pepper, then remove and keep warm.
Return the skillet to high heat with a little oil and add the marinated steak in a single layer; sear 2–3 minutes, toss and cook another 2–3 minutes until cooked through. If any marinade remains, pour it in and cook 1 minute more. Remove and keep warm with the vegetables.
Make the peanut sauce: combine coconut milk, 3/4 cup creamy peanut butter, 1/4 cup brown sugar, 2 tablespoons soy sauce, and 2 teaspoons Thai red curry paste in a medium saucepan over medium heat; stir and bring to a low boil until smooth and combined.
Assemble bowls by dividing scraped spaghetti squash among bowls, topping with bok choy and mushrooms, then the sliced steak. Drizzle with peanut sauce and finish with chopped peanuts, sliced chilies, shredded carrots, fresh mint, Thai basil, or chopped lemongrass as desired.