Bring a large pot of salted water to boil.
Cook the cauliflower until fork tender, about 10 minutes. Drain very thoroughly and return to the pot. Add the coconut oil and mash the cauliflower until smooth. Taste for seasoning and add more salt if needed.
Meanwhile, make the pesto: puree the scallions, pumpkin seeds, garlic, lemon juice, olive oil and ½ teaspoon salt until smooth.
Transfer the cauliflower mashed potatoes to a bowl and top with the pesto. Garnish with more pumpkin seeds and scallions and serve.