1. Rub the steak with the Brain Octane oil and set aside. Grate 2 teaspoons of zest from the lemon. Halve the lemon and cut into wedges. Squeeze out 1 teaspoon of juice and set the remaining lemon wedges aside.
2. In a small bowl, combine the lemon zest, butter, chives, herbs, and 1 teaspoon sea salt, stirring well to combine and create a compound butter. Stir in the lemon juice.
3. Heat a grill pan over (or fire up your grill to) medium-high heat. Season the steak with sea salt, place on the grill, and reduce the heat to medium-low.
4. Cook, taking care not to char the meat, for 5 to 6 minutes per side for rare, 6 to 7 minutes per side for medium-rare. Transfer the steak to a plate, top with 2½ tablespoons compound butter (reserve remaining compound butter for another use), and allow to rest for 5 minutes.
5. Slice the steak thinly across the grain, and serve with the spinach, topping with meat juices and a squeeze of lemon.