In a large pot set over medium heat, melt together the butter, shallot, garlic, thyme, lemon zest and a big pinch of red pepper flakes. Cook until the butter is browning and the garlic is fragrant, about 3 minutes. Stir in the pasta and toss to coat in the lemony butter. Stir in the zucchini and broth. Season with salt and pepper. Bring to a boil over high heat. Simmer 5-8 minutes until the pasta is al dente, stirring often.Stir in the ricotta, fontina, and basil. Cook another few minutes until very creamy and the basil is wilted. It should be creamy, but with just a touch of liquid.Divide the pasta among bowls and top with fresh thyme, basil, and chili flakes. Enjoy immediately!