COOK IT.
In a large cast iron pan, heat canola oil until smoking. Once smoking, add peppers, onion, and mushrooms and cook on high heat, stirring occasionally, for 5-7 minutes or until veggies char on edges. Add garlic and butter, cook 3-4 more minutes. Set aside.
Grill venison tenderloin over high heat for 2-3 minutes per side, or until medium-rare. Set aside and let rest.
Place the cast iron with peppers and onions back on heat while charring bread on the grill grates. Add bleu cheese to mixture and toss while cooking until just beginning to melt. Remove charred bread from grill.
Slice tenderloin into quarter-inch wide slices and place on bottom half of hoagies. One sliced tenderloin per sandwich. Add pepper and mushroom mixture on top. Smear generous amount of mustard on top half of bun, assemble, slice in half if desired, and enjoy!