Burger patties: In a large bowl, combine ground bison, egg whites, barbecue sauce, Dijon mustard, bulgur, steak spice, salt, black pepper, cayenne pepper, and capsicum by hand (mixing by hand instead of a spoon will produce a juicier burger). When well-combined, form into 8 patties and refrigerate until ready for cooking.
Oven fries: Preheat oven to 220 degrees celsius. Wash potatoes (do not peel) and cut into french-fry shaped strips. Toss in olive oil, 1/2 tsp each of cayenne and dried herbs. Spread on a large cookie sheet and bake for 45 minutes. Meanwhile, saute sliced mushrooms and onions in cooking spray, adding Worchestershire sauce when the mushrooms' water has evaporated and they are slightly browned. Add salt and pepper to taste. Keep warm until ready to serve.
Make dip for fries: Combine 2/3 of the drained yogurt, 2 tbsp of the mayonnaise, green onion, fresh herbs, and onion powder. Add ground black pepper to taste. Refrigerate until ready to use.
Cook burgers: Grill burger patties on a medium grill until medium-well, about 7 minutes per side, topping with sliced cheese for last two minutes of cooking. Lightly toast buns on grill for last minute of cooking.
Assemble burgers: Top each bun with one patty, a couple of spoonfuls of mushrooms and onions, and let your guests garnish with their choice of fresh spinach leaves, pickles, tomato slices, mustard, ketchup, low-fat mayo, and anything else you want to offer.
Serve fries hot out of the oven and tossed with black pepper and chopped parsley, with green-onion dip on the side.