Bring a large pot of salted water to a boil and cook the fusilli pasta according to package instructions until al dente.
While the pasta is cooking, heat a large skillet over medium heat.
Add the olive oil to the skillet and heat until shimmering.
Add the garlic to the skillet and cook until fragrant, about 1 minute.
Add the canned tuna with its oil to the skillet and break it up into small pieces with a wooden spoon.
Add the chopped olives, capers, and crushed red pepper flakes (if using) to the skillet and cook for 5-7 minutes until the flavors are combined.
Reserve some of the pasta cooking water and drain the fusilli pasta.
Add the cooked fusilli to the skillet with the sauce and toss to combine.
If the sauce seems too thick, add a few tablespoons of the reserved pasta cooking water to the skillet to loosen it up.
Season the pasta with salt and pepper to taste.
Serve the fusilli with tuna and olives hot, garnished with grated Parmesan cheese, if desired.