Preheat oven to 400ºF. Bring a pot of salted water to a boil. Line a baking sheet with heavy-duty aluminum foil. On sheet, toss cauliflower with 2 Tbsp. oil and sprinkle with salt. Roast until cauliflower is soft, 15 to 20 minutes, stirring once or twice while cooking.
Cook pasta in boiling water until al dente, about 10 minutes or as package label directs. While pasta is cooking, warm remaining 1 Tbsp. oil in a large skillet over medium-high heat. Add garlic and sauté until fragrant, about 30 seconds. Add kale and cook, stirring, until wilted, 1 to 2 minutes. Reduce heat to medium-low and add cream, lemon zest and juice, 1/4 tsp. salt and red pepper, if desired. Cook, stirring, until mixture is just bubbling, about 2 minutes.
Drain pasta, reserving 1/2 cup cooking water. Stir pasta into skillet to coat with sauce. Stir in cauliflower, ricotta and Parmesan. If mixture seems dry, stir in reserved cooking water 1 Tbsp. at a time to reach desired consistency. Season with salt and serve.