In a saucepan add 3 Tbsp of Oil over medium-high heat. Add in 2 cups of finely diced mushrooms and cook for a few mins until softened.
Reduce to medium heat and add in 1 Tbsp minced garlic, 1 tsp of salt, 1 tsp onion powder, ¼ tsp cayenne, 1 tsp smoked paprika, and ¼ cup packed brown sugar. Stir for a few mins until bubbling - then add in a bit of cornstarch or xanthan gum slurry to thicken, and set aside to cool.
Sear striploin in a hot steel pan, seasoned with salt and pepper until desired doneness, then let rest.
Toast your bread and brush the top side with mayo or your sauce of choice. Lather the base with mushroom jam, sliced steak, pickled onions, jalapeños, lettuce, and whatever other toppings you want.
