Add sardines with their oil to a bowl; add minced garlic, red pepper flakes, half the Italian parsley, and the ¼ cup olive oil. Use a fork to mash the mixture into a coarse paste. Reserve in the refrigerator until needed.

Add bread to a skillet, and drizzle olive oil evenly over the top, reserving 1 tablespoon for later. Add a pinch of salt, and set the heat to medium-high. Cook, stirring and tossing, until the edges of the bread start to turn golden brown. Reduce the heat to medium, and continue cooking until bread pieces are nicely browned and crispy on the outside, but still retain a slight bit of chewiness in the center of the larger pieces. Add remaining 1 tablespoon olive oil and garlic, and cook, stirring, for another 30 to 45 seconds. Remove from heat, transfer into a bowl, and reserve until needed.

Bring a large pot of salted water to a boil, add spaghetti, and cook until tender yet firm to the bite, about 12 minutes. Do not drain.

Meanwhile, for sauce, place the same skillet used for frying the bread back on the stove over medium-high heat. Transfer in the sardine mixture. As soon as it starts to bubble give it a stir, and cook for about 30 seconds, then turn off the heat.

Use tongs to transfer cooked noodles into the pan. It's fine if some water comes along; it helps to make the sauce. Turn the heat back on to low, and use tongs to mix noodles into the sauce, until everything is evenly combined. Transfer in about ¼ cup pasta water, and stir to combine. Add another ¼ cup, and repeat this process for a saucier, creamier texture. Additional pasta water can be added to adjust to your liking.

Turn off the heat; add remaining parsley, Parmesan cheese, and half the fried bread pieces. Drizzle in a little more olive oil. Toss until evenly mixed. Taste, season with salt if needed, and serve immediately. Garnish each serving with grated Parmesan, and crumble remaining fried bread pieces over the top. Finish with a sprinkle of parsley.