• Add 10 cups water and 2 tsp salt to a large pot (use same for 4 ppl). Cover and bring to a boil over high heat.
• Meanwhile, cut cauliflower into bite-sized pieces.
• Peel, then cut half the onion (whole onion for 4 ppl) into 1/4-inch pieces.

• Add cauliflower and 1 tbsp (2 tbsp) oil to an unlined baking sheet.
• Season with half the garlic salt and pepper, then toss to coat.
• Roast in the middle of the oven until golden-brown, 14-16 min.
• Meanwhile, pat chicken dry with paper towels. Season with salt and pepper.
• Heat a large non-stick pan over medium-high heat. When hot, add 1/2 tbsp (1 tbsp) oil, then chicken. (NOTE: Don't crowd the pan; cook chicken in 2 batches if needed.) Cook until golden, 1-2 min per side. 
• Transfer chicken to another unlined baking sheet. Roast in the top of the oven until chicken is cooked through, 12-14 min.**

• Meanwhile, add rigatoni to the boiling water.
• Cook uncovered, stirring occasionally, until tender, 10-12 min.
• Reserve 1/2 cup (1 cup) pasta water, then drain and return rigatoni to the same pot, off heat.

• Reheat the same pan (from step 2) over medium.
• When hot, add 1 tbsp (2 tbsp) butter, then onions. Cook, stirring often, until softened, 3-4 min.
• Sprinkle flour and remaining garlic salt over onions.
• Cook, stirring often, until onions are coated, 1 min.
• Add cream and 1/2 cup (1 cup) milk, then bring to a boil.
• Once boiling, cook, stirring often, until sauce thickens, 1 min.
• Remove from heat, then add spinach. Stir until wilted, 1 min.

• Add cheese, sauce, half the reserved pasta water and cauliflower to the pot with rigatoni.
• Stir until cheese melts, 1 min. (TIP: For a lighter sauce consistency, add more reserved pasta water, 1-2 tbsp at a time.)
• Season with salt and pepper, to taste.

• Thinly slice chicken.
• Divide cheesy creamy cauliflower pasta between bowls.
• Top bowls with chicken.
• Sprinkle 1/4 tsp (1/2 tsp) chili flakes over top. (NOTE: Reference heat guide.)

If you've opted to add chicken breasts, pat dry with paper towels. Season with salt and pepper. Heat a large non-stick pan over medium-high heat. When hot, add 1/2 tbsp (1 tbsp) oil, then chicken. (NOTE: Don't crowd the pan; cook chicken in 2 batches if needed.) Cook for 1-2 min per side, until golden. Transfer chicken to another unlined baking sheet. Roast in the top of the oven until chicken is cooked through, 12-14 min.** Use the same pan to cook sauce in step 4.

Thinly slice chicken. Top bowls with chicken.