1. Soak chiles in warm water for 10 minutes; drain.
2. Place arugula, radicchio, and endive in a large bowl; toss gently to combine.
3. Heat oil in a large skillet or wok over medium-high heat. Add garlic, fennel seeds, if desired, and chiles; stir constantly for 30 seconds. Reduce heat to low; cook 1 minute. Stir in mirin and salt; increase heat to high. Bring to a boil; boil for 15 seconds. Remove chiles from mixture. Drizzle hot dressing over greens; toss gently to coat. Serve salad immediately.