01 - Preheat grill to medium-high heat. Lightly oil the grill grates with vegetable oil to prevent sticking.
02 - Place beef bratwursts on the grill. Grill for 12-15 minutes, turning occasionally, until evenly browned and internal temperature reaches 160°F.
03 - During the last 2 minutes of grilling, place 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, mustard, sliced red onions, and chopped parsley if desired. Serve immediately while hot.