Before starting, add 10 cups warm water and 1 tbsp salt (use same for 4 ppl) to a large pot. Cover and bring to a boil over high heat. Wash and dry all produce. Thinly slice chives.Roughly chop spinach.Drain, then pat roasted peppers dry with paper towels. Roughly chop.

Pat chicken dry with paper towels, then cut each tender into 1-inch pieces.Season with garlic salt and pepper.

Heat a large non-stick pan over medium-high heat. When hot, add 1 tbsp butter, then chicken. (NOTE: Don't overcrowd the pan; cook in 2 batches if needed, using 1 tbsp butter per batch.) Cook, flipping occasionally, until cooked through, 5-6 min.**

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

Add onions to the pan with chicken. Cook, stirring occasionally, until softened, 3-4 min. Sprinkle flour over onions and chicken. Cook, stirring often, until coated, 1 min. Add cream and reserved pasta water, then bring to a boil. Cook, stirring often, until sauce thickens, 2-3 min.

Add chicken and cream sauce, cheese, spinach, roasted peppers and 1 tbsp (2 tbsp) butter to the pot with rigatoni. Stir until cheese melts, 1 min. Divide rigatoni between bowls.Sprinkle chives and chili flakes over top, to taste.