Preheat the oven to 425. Line a rimmed baking sheet with parchment paper and set aside.
Place the potatoes in a microwave safe bowl with the water and cover with a plate or safe lid. Microwave until the potatoes are fork tender--about 12 minutes total, but check yours at about 6 minutes and go from there.
Once the potatoes are just tender but not falling apart, drain the water and transfer them to the baking sheet. Use the bottom of a glass or jar to flatten them slightly.
Toss with avocado oil and salt and bake until golden on the edges--about 15 to 20 minutes. Check yours at 12 minutes and go from there.
Once golden brown, remove from the oven and pour over the butter and rosemary and toss while the potatoes are still hot. Serve warm.