01 - Preheat grill to medium-high heat. Lightly oil the grill grates with vegetable oil.
02 - Place beef bratwursts on the grill. Grill for 12–15 minutes, turning occasionally, until evenly browned and internal temperature reaches 160°F (71°C).
03 - During the last 2 minutes of grilling, place the buns on the grill to toast lightly. If using cheese, add a slice to each brat and let melt slightly.
04 - Warm sauerkraut in a small pan over medium heat or in the microwave until heated through.
05 - Place each grilled bratwurst in a toasted bun. Top generously with sauerkraut, a drizzle of mustard, sliced red onions, and chopped parsley, if desired.
06 - Serve immediately while hot.