Bring a pot of water to a boil and add 1 teaspoon of salt. Add the mushrooms and cook for about 5 minutes, just until tender. Drain well and let any excess moisture escape.
Heat 2 tablespoons of oil in a skillet over medium heat. Add the chopped onion and cook for about 5 minutes, stirring occasionally, until softened and translucent.
Transfer the warm onion to a large bowl. Add the chopped bell pepper, ground coriander, vinegar, soy sauce, and sugar. Stir until the sugar dissolves and everything is well combined.
Add the drained mushrooms, paprika, sesame seeds, minced garlic, and chili. Gently toss until the mushrooms are evenly coated in the marinade.
Heat the remaining 2 tablespoons of oil until shimmering. Carefully pour the hot oil over the garlic and spices in the mushroom mixture, then stir gently to combine.
Stir in the chopped parsley and black pepper. Taste and add more salt only if needed.
Cover and refrigerate for at least 2 hours so the mushrooms can absorb the marinade and the flavors have time to deepen. Serve chilled or slightly cool.