Remove the ribeye steak from the refrigerator 30 minutes before cooking to bring it to room temperature, ensuring an even cook.
Pat the steak extremely dry on all sides with paper towels; moisture is the enemy of a good crust.
Season both sides of the steak generously with the sea salt and black pepper.
Heat a cast-iron skillet over medium-high heat until it is ripping hot, then add the avocado oil.
Place the steak in the pan and sear for 3-4 minutes without moving it, until a deep golden-brown crust forms.
Flip the steak and immediately add the smashed garlic clove and rosemary sprig to the pan.
Tilt the pan slightly and use a spoon to baste the steak with the hot infused oil for the final 2-3 minutes of cooking.
Remove the steak from the pan and transfer to a cutting board to rest for at least 5-8 minutes.
While the steak rests, add the asparagus spears to the same pan and sauté in the residual juices for 3-4 minutes until crisp-tender.
Finish the asparagus with a squeeze of fresh lemon juice and serve alongside the sliced ribeye.