Roast the potatoes. Preheat the oven to 450°F. Toss the potatoes, olive oil, garlic (and salt and pepper to taste) on a sheet pan until evenly coated. Bake for 15-20 minutes or until the potatoes are golden brown and tender when pierced with a knife.
Make the pesto. Chop the dandelion greens down a bit and put in a blender (or food processor fitted with the steel blade attachment) with the pepita seeds, sunflower seeds and garlic and pulse until finely chopped.
With the motor on, drizzle in the olive oil in a thin stream.
Add the sea salt, pepper, lemon, and nutritional yeast (or Parmesan cheese), and pulse a few more times to combine. If the mixture seems very thick, add 1-2 tablespoons of water to thin to your desired thickness.
Taste for seasoning and add additional salt to taste. This will keep well in the fridge, in a tightly sealed container, for a few days; top the pesto with a layer of olive oil to decrease any browning.