Place peppers evenly in a single layer on a foil-lined baking sheet.
Place under broiler on the top rack. Watch them closely as the skin will blister and turn black within minutes. Turn the peppers after 5 minutes to blister all sides evenly. When done, the pepper skins should be evenly blistered and mostly black.
Adjust oven temperature to bake at 400°F.
Using 2-3 tbsp of oil, thoroughly brush both sides of each tortilla with oil. Arrange tortillas, overlapping, on a rimmed baking sheet (you may need to do 2 batches). Bake tortillas in 400°F oven until warm and pliable, about 5 minutes. Remove tortillas from the oven and keep warm.
Adjust oven to 350°F.