In a large pot of boiling salted water, cook pasta 3 minutes less than package instructions. Add sun-dried tomatoes, and cook 3 minutes. Remove 2 cups pasta water; reserve. Drain and return pasta mixture to pot.
Meanwhile, heat a small skillet over medium heat. Add almonds and cook, stirring occasionally, until lightly browned and fragrant, 2 to 4 minutes. Transfer to a small bowl; reserve. Return skillet to medium heat; add oil, garlic, and red-pepper flakes. Cook, stirring occasionally, until fragrant, 20 to 30 seconds. Remove from heat.
To pasta mixture in pot, add garlic mixture, reserved pasta water, cheese, and parsley. Season with salt and pepper; stir to combine. Let stand until slightly thickened, about 5 minutes. Divide pasta among four shallow dishes; sprinkle with almonds and, if desired, additional cheese.
For a spicier dish, increase the amount of red-pepper flakes to 1/2 teaspoon.