Preheat your oven to 400°F (200°C). Dice the red potato into 1/2-inch cubes and mince the garlic cloves.
Toss the potato cubes with half of the avocado oil, half of the minced garlic, and a pinch of sea salt and pepper on a baking sheet.
Roast the potatoes for 20-25 minutes, flipping halfway through, until they are golden and crispy.
While the potatoes roast, season the lamb steak with the remaining sea salt and black pepper.
Heat the remaining avocado oil in a cast-iron skillet over medium-high heat. Add the lamb steak and the rosemary sprig to the pan.
Sear the lamb for 3-4 minutes per side for medium-rare, basting with the rosemary-infused oil. Remove from heat and let rest for 5 minutes.
Steam the green beans for 4-5 minutes until tender-crisp and bright green.
Plate the lamb steak alongside the garlic potatoes and green beans, garnishing with the roasted rosemary if desired.