Fill a pot for the pasta with about 6 quarts of water, place over high heat, and bring to a boil.
Peel the tomatoes and coarsely chop them.
Peel the garlic and finely chop it. Finely chop enough parsley to measure about 2 tablespoons. Put the garlic, parsley, and olive oil in a 12-inch skillet and place over medium-high heat. When the garlic is sizzling, add the tomatoes. Season with salt and cook until the liquid the tomatoes released has evaporated, 10 to 12 minutes.
While the tomatoes are cooking, slice the flesh of the olives away from the pits into slivers. When the tomatoes are almost ready, add about 2 tablespoons salt to the boiling pasta water, add the spaghetti, and stir until all the strands are submerged. Cook until al dente.
When the tomatoes are ready, add the olives, cook for 1 to 2 more minutes, then remove from the heat.
When the pasta is done, drain well, toss with the sauce, and serve at once.