Add the potatoes and 1/4 cup salt to a large stockpot fitted with a strainer filled with water. Bring to a boil, then reduce to a simmer. Cook the potatoes until fork-tender, about 20 minutes. Using the strainer, remove the potatoes from the water and set aside to drain.
Add 1/4 cup oil to a baking sheet and coat generously. Gently dump or transfer the potatoes to the baking sheet using tongs. Smash the potatoes with a potato masher until the tops crack open. Drizzle with oil and season with salt and pepper.
Bake until golden brown, about 30 minutes. Transfer the potatoes to a platter. Top with chimichurri as desired.
Add the garlic, cilantro and parsley to a medium bowl and stir to combine. Add enough oil for the desired consistency. Season with salt. Set aside.