Before starting, preheat the oven to 450°F. Wash and dry all produce. Cut cauliflower into bite-sized pieces. Add cauliflower and 1 tbsp oil (dbl for 4 ppl) to an unlined baking sheet. Season with salt and pepper, then toss to coat. Roast in the middle of the oven, stirring halfway through, until golden-brown, 17-18 min.

While cauliflower roasts, peel, then mince or grate garlic. Heat a large non-stick pan over medium heat. When hot, add panko to the dry pan. Cook, stirring often, until toasted, 2-3 min. Remove the pan from heat, then transfer panko to a plate. Set aside. Carefully wipe the pan clean.

Heat the same pan over medium-high. When hot, add 1 tbsp oil (dbl for 4 ppl), then onions. Cook, stirring occasionally, until slightly softened, 3-4 min. Add shredded beef, broth concentrate, BBQ sauce and half the garlic, then season with salt. Cook, breaking up beef and stirring occasionally, until beef heats through, 3-4 min.** (NOTE: If the beef mixture is dry, add 2 tbsp water [dbl for 4 ppl], then stir to combine.)

While beef cooks, add horseradish, mustard and half the mayo to a small bowl. Season with salt and pepper, then stir to combine.

Halve buns, then arrange on another unlined baking sheet, cut-side up. Toast buns in the top of the oven until golden, 2-3 min. (TIP: Keep an eye on the buns so they don't burn!)

Combine remaining mayo and remaining garlic in a large bowl. Add cauliflower, then stir to coat. Sprinkle panko over cauliflower, then stir to coat. Season with salt and pepper, to taste. Spread horseradish sauce over buns. Stack spring mix and shredded beef mixture on bottom buns. Close with top buns. Divide beef sammies and cauliflower 'frites' between plates.