Mushroom Adobo

Name: Mushroom Adobo
Cuisine: Asian
Ingredients: 1 Tbsp. light or dark brown sugar; ½ cup unseasoned rice vinegar (such as Marukan); ½ cup tamari (such as San-J); 10 garlic cloves, peeled (not smashed); 3 dried bay leaves; 1 Tbsp. black peppercorns; 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt; 1 tsp. cornstarch; 2 tsp. mushroom bouillon powder (such as Lee Kum Kee); 1½ tsp. freshly ground black pepper; 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, plus more; 2–3 Tbsp. refined coconut oil or vegetable oil; 1½ lb. mixed mushrooms (such as hen of the woods, king oyster, and/or pioppino), torn into 2" pieces if large; Steamed jasmine rice (for serving); 2–3 oz. watercress or baby arugula (optional)