Feel free to substitute or add whichever seasonal vegetables you have on hand. Slideshow: More Macaroni and Cheese Recipes
Preheat the oven to 375°F.
In a large heavy skillet, heat the oil over medium heat until hot. Stir in the zucchini, garlic, 3/4 teaspoon salt and 1/2 teaspoon pepper, and cook, stirring occasionally until the zucchini is tender and the garlic is pale golden, 4 to 5 minutes. Remove the skillet from the heat and stir in the yogurt. Season with salt and pepper to taste.
In a large pot of boiling salted water, cook the spaghetti until al dente. Reserve 1/2 cup of the pasta cooking water, then drain the pasta. Toss the pasta with the zucchini mixture in the skillet along with 1/4 cup of the pasta cooking water. Add more pasta cooking water for a thinner sauce. Transfer the pasta to a 3 quart baking dish and sprinkle with the cheese. Bake the mac n cheese until the cheese is melted, about 10 minutes.