Preheat the oven to 375 degrees F.

Rub the cleaned Portobellos with 1 tablespoon oil and 1 teaspoon sea salt. Place on a baking sheet and bake for 5 minutes. Set aside.

Add 1 tablespoon of oil to a sauté pan. On medium heat, cook the onions and dates with 1 tablespoon salt and 1 tablespoon pepper. Cook for 10 minutes. Pour into a bowl and set aside.

Using the same sauté pan as you did for the onions, cook the bison patties for 3 minutes on each side on medium-high heat and set aside.

In a small bowl, place the arugula, 1 teaspoon avocado oil, 1 teaspoon sea salt and 1 teaspoon pepper. Mix gently.

To assemble the burger, place 1 Portobello, cap side down on a plate. Place a burger patty on the mushroom. Top patties with the onion-date mix and some arugula mix. Repeat with remaining patties. Enjoy!