Pangrattato: Dice the bread into small pieces (at least 1/2 cup). Spray generously with oil. Heat a large skillet over medium-high heat. Add bread pieces and sauté for about 2 minutes until golden brown. Remove to a bowl, sprinkle with salt, and set aside.

Return the skillet to the stove. Melt the butter with the olive oil over medium heat. Add the smashed garlic cloves and cook for 1 minute until fragrant.

Add the cauliflower florets to the skillet. Cook, stirring occasionally, for about 3 minutes. Add the sliced red onion, salt, and pepper.

Continue cooking for another 5-7 minutes, until the cauliflower is beautifully golden brown but still slightly firm. Remove and discard the smashed garlic cloves.

Meanwhile, cook the fettuccine in salted boiling water until 1 minute less than the packet's recommended time (al dente). Reserve about 1/2 cup of pasta water before draining.

Add the drained pasta and lemon juice to the skillet with the cauliflower. Toss well to combine, adding a splash of reserved pasta water if needed to create a light sauce. Stir in red chili flakes and lemon zest.

Serve immediately, topped generously with the crispy pangrattato.