Before starting, preheat the broiler to high. Add 10 cups warm water and 2 tsp 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.Core, then cut pepper into 1/2-inch pieces. Add peppers and 1 tbsp oil (dbl for 4 ppl) to a foil-lined baking sheet. Season with salt and pepper, then toss to combine. Broil in the middle of the oven until golden-brown and tender, 5-8 min.

Meanwhile, pat chicken dry with paper towels, then cut each tender in half crosswise. 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 pasta water (dbl for 4 ppl). Drain and return rigatoni to the same pot, off heat.

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

Add chicken and cream sauce, cheese, reserved pasta water, spinach, roasted peppers and 1 tbsp butter (dbl for 4 ppl) to the pot with rigatoni. Stir until cheese melts, 1 min. Divide rigatoni between bowls.Sprinkle chives and chili flakes over top, to taste.