Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish with olive oil.

In a large pot, bring water to a boil and add salt. Blanch cauliflower florets for about 2 minutes, then drain and cool.

Heat olive oil in a large sauté pan over medium-high heat. Cook chicken sausage for 8-12 minutes until browned.

Add chopped onion, minced garlic, and thyme to the pan. Sauté for 5-6 minutes until the onion is translucent.

Hand-crush the whole peeled tomatoes and add them to the pan, letting the mixture simmer for 5 minutes.

Mix the sausage and tomato sauce with the blanched cauliflower. Transfer to the prepared baking dish.

Combine breadcrumbs and grated Parmesan in a bowl, then sprinkle over the casserole.

Bake in the preheated oven for 25 minutes until breadcrumbs are golden and sauce is bubbly. Let rest for 5 minutes before serving.