Preheat oven to 450 F. Lightly grease rimmed baking sheet.

In large pot, place potatoes and cover with cold water. Place pot over high heat and bring to a boil. Immediately reduce heat to medium-low and simmer potatoes until just cooked through and easily pierced with fork, about 15 to 25 minutes, depending on size of potatoes. Drain potatoes into colander and let sit for 5 minutes.

Transfer potatoes to prepared baking sheet and, using fork, potato masher, or mug, smash each potato, trying to keep them in one piece. Drizzle grapeseed oil over potatoes and brush to coat. Lightly season with 1/2 tsp salt and a good pinch of pepper before placing in oven. Roast potatoes, flipping once about halfway through cooking time, until crispy and golden brown, about 40 to 50 minutes, depending on size of potatoes.

Meanwhile, make walnut and red pepper salsa. In food processor, pulse together walnuts, olive oil, lemon juice, coconut sugar, red pepper flakes, and remaining 1/2 tsp salt until a chunky paste forms. Transfer to serving bowl and stir in chopped roasted red pepper and parsley. Set aside.

Serve warm potatoes alongside walnut and red pepper salsa.