1. Preheat oven to 375 degrees

2. Heat oil in 2-quart flameproof casserole dish over medium heat. Add onion, garlic, and pepper flakes; cook, stirring, until onion is softened, about 5 minutes. Add beef and cook, breaking it apart with spoon, until browned, about 10 minutes.

3. Stir penne, marinara sauce, 1/2 cup monterey jack, and the parsley into beef mixture and spread evenly; sprinkle with remaining 1/4 cup cheese. Transfer casserole to oven and bake until cheese is melted and filling is bubbly around the edge, about 20 minutes.