How to Make It
In a small bowl, combine the yogurt, lemon zest and 1 teaspoon of the olive oil and season with salt. Refrigerate until chilled.
Preheat the oven to 450°. On a baking sheet, toss the carrots with 1 tablespoon of the olive oil and the fennel and season with salt and pepper. Spread in an even layer and roast, stirring once, until lightly golden and tender, about 15 minutes.
In a large nonstick skillet, heat 1 tablespoon of the olive oil. Add the scallions and cook over moderate heat, stirring occasionally, until golden and tender, about 8 minutes. Transfer to a plate. Wipe out the skillet.
Heat 2 tablespoons of olive oil in the skillet. Add the peppers and cook over moderate heat, stirring occasionally, until golden, about 3 minutes. Add the chile and garlic and cook, stirring, until fragrant, about 1 minute. Stir in the roasted carrots and scallions and the lemon juice.
In a pot of salted boiling water, cook the garganelli until al dente. Drain, reserving 1/2 cup of the pasta water. Return the pasta and water to the pot. Add the roasted carrot mixture, the butter, remaining 2 tablespoons of olive oil and the 1/2 cup of cheese and season with salt and pepper; toss to coat. Transfer the pasta to bowls and garnish with grated cheese and the chopped carrot tops. Dollop the lemon yogurt on the pasta and serve.