Place the zucchini rounds on a baking sheet and toss together with enough olive oil to lightly coat, season with salt and pepper. Spread in an even layer and move the baking sheet to the oven. Bake for 15-20 minutes or until soft and starting to brown in spots.
Remove from the oven and set aside to cool.
Place the cream in a small sauce pan with the smashed garlic clove and thyme sprig. Bring to a low boil for about 20-25 minutes or until slightly thickened. Add the parmesan to the pot and stir until melted. Set over low heat to hold until ready to use.
Meanwhile fill a large pot with water and add 1 teaspoon of salt. Bring to a boil and then add the pasta to the water and cook according to the box instructions. Reserve 1 cup of the cooking water, drain the the noodles and place them back in the pot. Add the lemon juice to the cream mixture and pour it over the noodles along with the zucchini and 1/4 cup of the reserved cooking water. Toss everything together, taste and add more of the reserved cooking water if the pasta is too dry and more salt or lemon juice if needed. Serve immediately with extra parmesan.