Put olive oil and garlic in a medium saucepan over medium-high heat. When garlic begins to sizzle, add tomatoes and stir to combine. Decrease heat to medium and cook, stirring occasionally, for 4 minutes. Flake tuna into the sauce with a fork. Cook for 2 minutes longer, until warmed through, and then add parsley (and capers, if using). Taste and season with salt and freshly ground black pepper, as needed. Cover and keep warm.

Bring a large pot of salted water to a boil over high heat. Add pasta and stir well to prevent sticking. Cook until pasta is done to your liking; drain, reserving a little of the cooking liquid.

Toss pasta with sauce and add reserved cooking liquid as needed. Sprinkle lemon juice into bowl and toss thoroughly. Serve at once.