01 - Preheat grill to medium-high heat, approximately 400°F. Ensure grates are clean and lightly oiled to prevent sticking.
02 - Place sliced bell peppers and onions in a large bowl. Drizzle with olive oil and season generously with salt and black pepper. Toss to coat evenly.
03 - In a small mixing bowl, whisk together Dijon mustard, honey, apple cider vinegar, and BBQ sauce until smooth and well combined. Set aside for glazing.
04 - Place beef sausages on the preheated grill. Cook for 10 to 12 minutes, turning every 3 to 4 minutes, until evenly browned and cooked through with an internal temperature of 160°F.
05 - Transfer seasoned peppers and onions to a grill basket or foil tray. Place on grill and cook for 8 to 10 minutes, stirring occasionally, until tender and slightly charred.
06 - During the final 2 minutes of cooking, brush sausages generously with the prepared mustard glaze. Turn once to coat evenly on all sides and allow glaze to caramelize slightly.
07 - Remove sausages and vegetables from grill. Arrange sausages on plates, top with grilled peppers and onions, and drizzle with any remaining mustard glaze. Serve immediately while hot.