Bring a 6- to 8-quart pot of well-salted water to a boil over high heat.
Heat the oil and garlic in a 12-inch skillet over medium-low heat. Cook for 2 minutes, pressing on the garlic with a fork to release its fragrance; don’t let it brown.
Stir in the olives, peppers, and sun-dried tomatoes and cook, stirring occasionally, until heated through, 3 to 4 minutes. Add the tomatoes and their juice and use the fork to crush them a bit. Raise the heat to medium high and bring to a simmer. Lower the heat to medium low and cook, stirring occasionally, until slightly thickened, about 10 minutes.
Add the tuna, breaking it up with the fork, and cook, stirring occasionally, until the sauce has thickened, 5 to 10 minutes. Remove the garlic and stir in the parsley.
Meanwhile, cook the pasta until al dente. Reserve 1/2 cup of the pasta water, then drain the pasta. Add the pasta to the sauce and toss to coat, adding a little of the reserved cooking water to moisten if necessary.