Wash and dry all produce. Preheat oven to 500 degrees or broiler to high with rack 3-4 inches from flame. Bring a large pot of salted water to a boil. Trim zucchini, then cut into 1/3-inch-thick rounds. Halve, peel, and finely dice onion. Trim, then thinly slice scallions, separating greens and whites. Mince or grate garlic.

Spread out zucchini on a lightly oiled baking sheet. Sprinkle with a large drizzle of oil and season with 1 tsp Tuscan heat spice (save the rest for step 4) and plenty of salt and pepper. Bake or broil until browned, 5-7 minutes. (TIP: Keep an eye out for any burning.) Transfer zucchini to a medium bowl and reduce oven temperature to 450 degrees.

Once water boils, add gemelli to pot. Cook until al dente, 9-11 minutes. Scoop out and reserve 1 cup pasta cooking water, then drain. Meanwhile, heat a drizzle of olive oil in a large pan over mediumhigh heat. Remove sausage from casings; discard casings. Add sausage to pan, breaking up meat into small pieces. Cook, tossing occasionally, until cooked through, 4-6 minutes. Remove from pan and set aside in another medium bowl.

Heat a large drizzle of olive oil in same pan over medium-high heat. Add onion and scallion whites. Cook, tossing, until softened, 2-3 minutes. Toss in garlic and remaining Tuscan heat spice. Cook until fragrant, about 1 minute. Add tomatoes, stock concentrate, and 1/2 cup pasta water. Bring to a boil, then lower heat and reduce to a simmer. Season with plenty of salt and pepper.

Place flatbreads on baking sheet used for zucchini. Spread about 1/3 cup sauce evenly over one flatbread; repeat with the other. Scatter mozzarella in an even layer over of each, then arrange half the zucchini and half the sausage on top. Bake in oven until cheese melts and crust is golden brown and crisp, 5-7 minutes. Cut into slices, scatter with half the scallion greens, and serve.

To prep lunch, place pan with remaining sauce over medium-low heat. Stir in 2 TBSP butter and sour cream. Add more pasta water, if needed, to loosen. Stir in gemelli along with remaining sausage, zucchini, and scallion greens. Divide between reusable plastic containers. Pack with Parmesan and keep refrigerated. When ready to eat, microwave on high for 2-3 minutes, then sprinkle with Parmesan.