In bowl, combine mayonnaise, onions, cheeses, Monterey Jack cheese, salsa and fajita marinade; mix well.
Transfer mixture to an ungreased 9-inch pie plate or 1-quart casserole. Bake, uncovered, in a 350 degree F oven for 15 to 20 minutes or until bubbly around edges. Serve warm with Baked Tortilla Chips. Garnish with lime wedges.
To serve with tortilla wedges: Cut five 6-inch flour tortillas into wedges. Place in single layers on ungreased baking sheets. Bake in a 350 degree F oven for 10 to 15 minutes, or until lightly browned and crisp.
To create phyllo cups as pictured: Bake mixture for 10 minutes in a 1-quart casserole. Then spoon 1 tablespoon mixture into each phyllo shell. Bake for 5 more minutes or until heated through and bubbly.