Preheat your oven to 400°F and line a baking sheet with parchment paper.
Slice the zucchini into half-inch thick rounds and toss them on the baking sheet with 0.5 tbsp of avocado oil and half of the sea salt and black pepper.
Roast the zucchini for 15-18 minutes, flipping halfway through, until they are tender and lightly caramelized.
While the zucchini roasts, pat the sirloin steak completely dry with paper towels and season both sides with the remaining salt and pepper.
Heat the remaining 0.5 tbsp of avocado oil in a cast-iron skillet over medium-high heat until the oil is shimmering and just starting to smoke.
Place the steak in the skillet and sear for 3-4 minutes per side for medium-rare, ensuring a deep brown crust forms.
In the final minute of searing, add the ghee, minced garlic, and rosemary to the pan, tilting the skillet to spoon the melted herb butter over the steak.
Remove the steak from the pan and let it rest on a cutting board for 5 minutes to lock in the juices.
Slice the steak against the grain and serve immediately alongside the warm roasted zucchini rounds.