Heat broiler to high or oven to 500 degrees. Bring a large pot of salted water to a boil. Wash and dry all produce. Trim and quarter zucchini lengthwise; cut crosswise into 1/2-inch-thick pieces. Place 1 TBSP butter (2 TBSP for 4) in a medium microwave-safe bowl; microwave in 10- 15 second intervals until melted. Stir in panko; season with salt and pepper.

Pat chicken dry with paper towels. Heat a large drizzle of olive oil in a large, preferably ovenproof, pan over medium-high heat. Add chicken; season with salt, pepper, and half the Tuscan Heat Spice. Cook, stirring occasionally, until browned and cooked through, 4-6 minutes. Turn off heat; transfer to a second medium bowl. Wipe out pan.

Once water is boiling, add penne to pot. Cook until al dente, 9-11 minutes. Reserve 1 cup pasta cooking water, then drain.

Meanwhile, heat another large drizzle of olive oil in pan used for chicken over medium-high heat. Add zucchini and remaining Tuscan Heat Spice; cook, stirring occasionally, until golden brown and tender, 6-8 minutes. Reduce heat to medium low.

Add marinara sauce, stock concentrate, and chicken to pan. Stir in drained penne, 1/4 cup reserved pasta cooking water (1/2 cup for 4 servings), and 2 TBSP butter (3 TBSP for 4). (TIP: If needed, stir in more reserved cooking water 1 TBSP at a time until penne is thoroughly coated in sauce.) Season with salt (start with 1/2 tsp, taste, and add more from there) and pepper. TIP: If your pan isn’t ovenproof, transfer mixture to a baking dish.

Sprinkle pasta mixture with mozzarella and panko. Broil or bake until cheese is melted and bubbly and panko is golden, 2-4 minutes. (TIP: Watch carefully for any burning.) Serve straight from the pan.