Serve with Glazed Baby Carrots. Chimichurri--the South American herb sauce typically served with meat--revs up basic mac and cheese with tangy flavors. You can also serve this in individual ramekins or small serving skillets.
Cook pasta according to package directions, omitting salt and fat; drain.
While pasta cooks, combine milk, stock, flour, and salt in a medium saucepan, stirring with a whisk. Bring to a boil over medium heat; cook 1 minute or until thickened. Let stand 5 minutes. Add 2 ounces shredded cheddar and processed cheese, stirring until smooth.
Heat a 10-inch cast-iron skillet over medium-high heat. Add oil; swirl to coat. Add onion, oregano, thyme, pepper, and garlic; cook 3 minutes, stirring occasionally. Combine onion mixture, parsley stems, cilantro stems, and lime juice in a food processor; pulse until coarsely chopped.
Combine pasta, milk mixture, and parsley mixture. Heat cast-iron skillet over high heat. Coat pan with cooking spray. Add pasta mixture to pan; sprinkle with remaining 1/2 ounce cheddar cheese. Broil 8 inches from heat for 5 minutes or until cheese is browned. Sprinkle with cilantro leaves.