Preheat the oven to 425°F (220°C). Toss the cauliflower florets with olive oil, salt, and pepper. Spread them on a baking sheet and roast for 20-25 minutes until golden and tender.

In a large pot, bring salted water to a boil. Add the spaghetti and cook according to package instructions until al dente. Reserve 1 cup of pasta water, then drain the pasta.

In a mixing bowl, combine the chopped Swiss chard, minced garlic, lemon zest, olive oil, lemon juice, salt, and pepper. Mix well to combine.

In the pot with the drained pasta, add the roasted cauliflower and gremolata. Toss everything together, adding reserved pasta water as needed to create a light sauce. Serve with grated parmesan cheese if desired.