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Add pasta to a large pot of salted boiling water and cook until al dente according to the directions on the packet. Pour pasta in a strainer, rinse with cold water to stop cooking, and drain well. Set aside.
In the same saucepan over medium heat, add a good drizzle of olive oil and the onion and garlic. Add salt and pepper, then mix. Cook 3 to 4 minutes, stirring regularly.
Add the chicken, broccoli, cauliflower, maple syrup, and Herbes de Provence, then salt and pepper to taste. Cook 7 to 8 minutes, stirring regularly. Separate meat into small chunks and drain well. Remove from heat, add 1 cup mozzarella, and mix. Set aside.
Melt the butter in a saucepan over medium heat, then add the garlic. Cook 2 to 3 minutes, stirring regularly.
Add flour and mix. Cook 2 minutes, stirring constantly.
Add milk, parmesan, and Herbes de Provence, then salt and pepper to taste. Stir with a whisk to ensure flour is well blended.
Bring to a boil, reduce heat to low, and cook 3 to 4 minutes, stirring regularly until sauce thickens slightly. Taste and adjust seasoning if necessary. Pour 1 cup (250 ml) of sauce onto stuffing and mix.
Preheat oven to 400°F (200°C).
Pour 1 or 2 ladlefuls of sauce into a large baking dish (or two) and spread evenly. Stuff pasta shells with chicken mixture and place in baking dish. Pour the rest of the sauce over the pasta shells, than top with mozzarella.
Broil for 10 minutes, then bake 2 or 3 minutes more until the cheese is golden. Serve immediately!