To make the breadcrumbs: in a large skillet, heat the olive oil over medium heat. Add the bread and cook, stirring occasionally, until bread is golden brown and toasted. Add the garlic and cook for 1 minute. Season with salt, to taste. Transfer to a bowl and set aside.

Bring a large pot of salted water to a boil. Cook the spaghetti until al dente, according to package instructions. Reserve 1 cup of the starchy pasta water and drain the pasta. Pour the pasta back into the pot.

While the pasta is cooking, whisk together the olive oil, lemon zest, lemon juice, and Parmesan cheese in a small bowl.

Pour the lemon sauce over the cooked spaghetti. Add the butter and toss until well combined, the butter will melt over the warm pasta. Add 1/4 cup of the reserved pasta water and toss again. If you think the pasta needs a little more liquid, you can add a little more of the water.

Season with crushed red pepper flakes, salt, and black pepper, to taste. Divide the pasta among bowls and garnish with fresh basil, extra Parmesan cheese, and the toasted breadcrumbs. Serve immediately.