Cauliflower is a packed with vitamin C, vitamin K, and folate. It's low in carbs and still packs a decent amount of good-for-you fiber.
Place cauliflower in a steamer basket in a large saucepan. Add water to saucepan to just below basket. Bring to boiling. Steam, covered, 8 to 10 minutes or until very tender.
Meanwhile, cook pasta in a large amount of boiling water 2 minutes less than package directions. Drain pasta and transfer to a large bowl.
Transfer cauliflower to a food processor or blender. Add milk, chipotle pepper, and adobo sauce. Cover and process or blend until smooth.
Dry large saucepan. Add oil and heat over medium. Add onion; cook 2 to 3 minutes or until tender, stirring occasionally. Add garlic; cook and stir 1 minute or until fragrant. Add spinach; cook 2 minutes or until slightly wilted. Reduce heat to medium-low. Stir in cauliflower mixture, mustard, and salt. Gradually whisk in cheeses just until melted.
Pour cauliflower mixture over cooked pasta; stir gently to combine. If desired, top with black pepper and paprika.