Bring a large pot of well-salted water to a boil. Add pasta and cook, uncovered, until just tender, 10 to 12 minutes. Meanwhile, put oil and garlic in a small frying pan and heat over medium heat. As soon as garlic begins to sizzle, remove pan from heat and set aside. Warm two pasta bowls between wet paper towels in a microwave, 20 seconds.
Drain pasta, reserving 1/2 cup pasta water, and return to pot. Pour garlic oil into pasta. Add lemon juice, salt, 2 pinches of chile flakes, and half of sea-urchin roe. Toss quickly with tongs to coat well, then swirl in the pasta cooking water.
Divide pasta between warmed bowls (including any liquid) and top with remaining roe, a pinch of chile flakes, and parsley.
*Good fish shops and Japanese markets will either carry sea-urchin roe or order it for you. You can also buy online from San Diego's Apex Wild Seafood (apexwildseafood.com; $46 for 120 grams of cleaned top-grade roe, about 15 pieces).