Place the potatoes in a large sauce pan and cover with cold water. Add the garlic, rosemary sprigs and lemon half to the water and season well with salt. Place over medium-high heat and bring to a boil. Reduce the heat to a simmer and cook until the potatoes are tender when pierced with a fork, about 15 minutes. Drain well and immediately cut the potatoes into halves. Place on a plate to allow the steam to escape. Allow to cool for 15 minutes.
Meanwhile, to make the seasoning salt, mix together the lemon zest, chopped rosemary and 1/2 teaspoon salt in a small bowl. Set aside
Heat a large skillet over medium-high heat. Add the oil and heat until it shimmers when it swirls in the skillet. Add the potatoes cut-side down to the skillet. Do not overcrowd the skillet. This may be done in 2 batches. Cook until the bottom of the potatoes are a deep golden brown, 3 to 4 minutes. Using a metal spatula, flip the potatoes and cook on the second side for an additional 3 minutes. Remove to a paper towel-lined plate and drain well. Sprinkle with the seasoning salt and serve warm.