Heat oven to 375 F.
In skillet over medium heat, heat oil. Add onion and cook, stirring until softened, about 5 minutes. Add chiles and tomatoes; simmer.
Reduce heat and stir in cubed cheese until smooth. Turn off heat; stir in cheddar and mozzarella until melted. Stir in jalapeno and half the pepperoni.
Garnish with remaining pepperoni.
Slice baguette into 1/2-inch slices. Place on baking sheet. Add butter to tops of slices. Toast in oven until tops are golden brown. Serve with dip.