Cook Pasta: Immerse the pasta in boiling salted water and cook until al dente according to package instructions.
Prepare Tuna Sauce Base: While pasta cooks, heat 2-3 tablespoons of olive oil in a pan over low heat. Press 1-2 cloves of garlic and add to the oil along with chopped bird's eye chili. Simmer gently for 2-3 minutes, stirring to infuse the oil.
Add Tuna: Add the tuna (canned or fresh) to the pan. Crumble and mix with the garlic and chili oil. If using fresh tuna, season with a pinch of salt; if canned tuna in olive oil or water, no additional salt is needed.
Add Olives and Lemon: Add about ten black olives cut in half. Add the zest of half a lemon and then squeeze the juice of half a lemon into the pan. Adjust lemon juice to taste if desired.
Add Pasta Water and Cheese: Add about one ladle of starchy pasta cooking water to the pan to loosen the sauce and make it creamier. Optionally, add freshly grated pecorino or parmesan cheese to chunk up the sauce.
Combine Pasta and Spinach: Turn off the heat. Drain the pasta and add it to the pan. Add a good handful of young spinach shoots and mix well so the spinach wilts quickly. Add a little more olive oil if needed to help cook the spinach and make the sauce creamy.
Serve: Serve immediately, optionally finishing with a drizzle of olive oil.