01 - Preheat grill to medium-high heat. Lightly oil the grill grates with vegetable oil using a paper towel or brush to prevent sticking.
02 - Place beef bratwursts on the preheated grill. Cook for 12-15 minutes, turning every 3-4 minutes, until evenly browned with a nice char and internal temperature reaches 160°F.
03 - During the final 2 minutes of grilling, place buns cut-side down on the grill to toast lightly until golden brown and crisp.
04 - If adding Swiss cheese, place a slice on each bratwurst during the last minute of cooking and close the grill lid briefly to melt.
05 - Transfer drained sauerkraut to a small saucepan and heat over medium heat for 3-5 minutes, stirring occasionally, until steaming hot. Alternatively, microwave in a microwave-safe bowl for 1-2 minutes.
06 - Place each grilled bratwurst in a toasted bun. Top generously with warm sauerkraut, drizzle with mustard, and add sliced red onions and chopped parsley as desired.
07 - Serve the brats immediately while hot, accompanied by potato salad, crispy fries, or your favorite sides.