Preheat oven to 350°F.
In a large bowl, beat cream cheese, Monterey Jack cheese, sour cream, Parmesan, and mustard with an electric mixer on medium speed until well combined.
In a 10-inch cast iron skillet, heat oil over medium-high heat. Add 2 cups of the Brussels sprouts and the onion; cook, stirring frequently, about 4 minutes or until sprouts are tender. Add the garlic and cook 1 minute more.
Remove from heat. Stir in the cheese mixture and artichoke hearts.
Bake, uncovered, 35 to 40 minutes or until lightly golden and bubbly. Top with remaining 1/2 cup Brussels sprouts. Serve with whole grain scoop-style tortilla chips and/or sweet pepper slices.