Heat a skillet over medium heat with some oil.
Brush the rest on the portobello mushroom caps and onion, sprinkling with sea salt. cook for 10-15 minutes, flipping once, until fully cooked through. Turn off heat and set aside to cool for a few minutes.
To make beef patties:
In a large, combine the ground beef, fresh herbs, and sea salt. Heat some of the cooking fat in a cast-iron skillet on medium heat. Cook the patties for about 5-8 minutes a side, until nicely browned on the outside and cooked throughout.
Grab a leaf or two of lettuce and construct a wrap with a beef patty, a tbsp of garlic mayo and some avocado slices.