01 - Preheat grill to medium-high heat, approximately 400°F.
02 - Toss sliced bell peppers and onions with olive oil, salt, and black pepper in a large bowl until evenly coated.
03 - Whisk together Dijon mustard, honey, apple cider vinegar, and BBQ sauce in a small bowl until smooth and well combined.
04 - Place beef sausages on the grill and cook for 10 to 12 minutes, turning occasionally until browned on all sides and cooked through to an internal temperature of 160°F.
05 - Add peppers and onions to the grill using a grill basket or foil tray. Cook for 8 to 10 minutes until tender and slightly charred, stirring occasionally.
06 - Brush sausages generously with the mustard glaze during the final 2 minutes of grilling, turning to coat evenly and allow the glaze to caramelize slightly.
07 - Transfer sausages to a serving platter, top with grilled peppers and onions, and drizzle with any remaining glaze if desired.