Add a swirl of oil to coat the bottom of a small skillet. Heat over medium flame until shimmering, then add the garlic . Cook 1 to 2 minutes, until garlic is lightly browned and fragrant. Remove from skillet, and save for another use.
Add the carrots to pan. Season with salt and pepper. Cook, stirring every now and again, until tender, about 5 minutes. Add the Swiss chard, and sauté until wilted, 2 to 3 minutes.
Stir in the mascarpone until melted, then stir in the pasta water.
Add the fennel fronds, pecorino, and season with salt and pepper again. Stir in the tortellini. Cook for 1 minute, until pasta is heated through. Serve immediately.