Cook the pasta al dente (the pasta should be slightly firm when bitten). If you're using pasta cooking water instead of the broth, remember to reserve 1/4 cup of the water.
Cut the chicken into 1-inch (2.5 cm) cubes, season with Herbes de Provence, salt and pepper. Cut the zucchini into 1/4-inch (1/2 cm) slices or half-slices.
Heat the oil in a large frying pan over high heat, add the chicken pieces. Don't stir for the first 2 minutes (letting the chicken brown), then cook for 2 more minutes, stirring from time to time, until the chicken is golden and almost completely cooked. Transfer to a plate.
Add the zucchini to the pan and cook it just like chicken. At first, do not stir for about 2-3 minutes, letting it brown, then stir and cook for another minute, the zucchini should still be slightly firm and not entirely cooked.
Move zucchini to the side of the pan, reduce the heat to low, and add finely chopped garlic. Cook for another 30 seconds, stirring constantly.
Add the flour and stir until it's combined with garlic and zucchini.
Add the cream and broth (or 1/4 teaspoon of crushed bouillon cubes + 1/4 cup pasta cooking water). Add the chicken back to the pan. Cook for 2-3 minutes over medium heat, until the sauce is slightly thickened. Take the pan off the heat.
Stir everything together, season with salt, pepper and lemon juice to taste.