Ingredients

• 3 Tbsp. fish sauce
• 1 cup unseasoned rice vinegar
• 1/4 cup sliced scallions
• 1 1/2" piece ginger, peeled, finely grated
• Kosher salt
• 2 Tbsp. Aleppo-style pepper or 1 Tbsp. crushed red pepper flakes
• 3/4 cup unsalted, roasted peanuts plus 1/4 cup crushed
• Kosher salt
• 1 lb. brussels sprouts, preferably small ones, trimmed, divided
• 1 cup vegetable oil
• 8 (6") corn tortillas
• 1/4 cup finely chopped white onion
• Sliced avocado, sliced serrano chiles, cilantro leaves with tender stems, flaky sea salt, and lime wedges (for serving)

Instructions

1. Heat a small saucepan over medium. When hot, pour in 1 Tbsp. fish sauce. It should bubble up vigorously and then get thicker and slightly darker, about 30 seconds. Repeat with remaining fish sauce, incorporating 1 Tbsp. at a time. Carefully add vinegar (it may spatter), then transfer mixture to a small bowl; let cool. Stir in scallions and ginger. Taste and season with salt.
2. Purée red pepper and 3/4 cup whole peanuts in a food processor until a smooth butter forms, about 2 minutes. Season with kosher salt and scrape into a small bowl.
3. Very thinly slice one-fourth of brussels sprouts; transfer to a medium bowl. Cut remaining brussels sprouts in half. Heat oil in a medium skillet over medium-high. Shallow-fry halved brussels sprouts in batches, being careful not to overcrowd the pan, until browned and crisp, about 5 minutes per batch. Transfer to paper towels to drain, then add to sliced brussels sprouts. Drizzle with vinaigrette and toss to coat; season with kosher salt.
4. To serve, heat a medium skillet over medium-high. Working one at a time, cook tortillas just until warmed through; transfer to plates. Spread tortillas with some spicy peanut butter; spoon brussels sprouts over. Top with onion, avocado, chiles, cilantro, and 1/4 cup crushed peanuts; sprinkle with sea salt. Serve with lime wedges.
5. Vinaigrette can be made 1 week ahead. Cover and chill.