For the fries:
Preheat oven to 450°F and cover a large baking sheet with parchment paper.
Peel cassava with a vegetable peeler to remove the waxy skin. Cut in half crosswise to make it easier to manage, then slice in half length-wise. Cut into ¼-inch thick fry strips.
Place fries in a large pot, cover with cold water, and add the 1/2 tsp salt. Bring to a boil and cook 10-15 minutes, or until tender. Drain fries and place in a large bowl. Toss with oil until coated, then spread in a single layer on the baking sheet.
Roast 10-15 minutes, until beginning to brown, then flip and roast an additional 10-15 minutes. When they're crisped the way you like them, remove from oven and sprinkle with paprika, cayenne and lime zest. Serve immediately.
For the sauce:
Place garlic, avocado oil, green onion, lime juice, cumin seeds, red pepper flakes and remaining sea salt in a food processor and puree until smooth. Serve at room temperature and later store covered in the fridge.