01 - Preheat grill to medium-high heat (approximately 375-400°F).
02 - Toss sliced bell peppers and onions with olive oil, salt, and black pepper in a large bowl until evenly coated.
03 - In a small mixing bowl, whisk together Dijon mustard, honey, apple cider vinegar, and BBQ sauce until smooth and well combined.
04 - Place beef sausages on the preheated grill. Cook for 10-12 minutes, turning occasionally, until browned on all sides and cooked through to an internal temperature of 160°F.
05 - Add seasoned peppers and onions to the grill using a grill basket or foil tray. Cook for 8-10 minutes, stirring occasionally, until tender and slightly charred.
06 - During the final 2 minutes of grilling, brush sausages generously with the mustard glaze, turning to coat all sides evenly.
07 - Transfer sausages to a serving platter, top with grilled peppers and onions, and drizzle with any remaining glaze if desired. Serve immediately while hot.