If using 10-inch tortillas, set 2 empty food cans 3 to 4 inches apart on a 14x17-inch foil lined baking sheet.
If using 12 or 13-inch tortillas, set 1 food can on baking sheet.
Drape a foil square over the top of each can.
Fill a pizza pan (one that's at least 3/4-inch deep) or another appropriately rimmed container with about 1/2 inch of warm water; add 1/4 teaspoon of olive oil.
Quickly immerse a tortilla in the water, then lift out and let drain.
Drape the damp tortilla over the foil on the empty food can (if you place it slightly off-center the shell with have a dramatic higher flair to one edge).
If you have room on the pan for another tortilla, add another 1/4 teaspoon oil to the water, dip a tortilla, and drape it over the other can.
Bake the taco salad shells in a preheated 450 degree F oven until they're lightly brown and firm enough to hold their shape, which will take about 4 to 5 minutes.
Using pot holders, carefully lift the shells off the cans and place them cup-side-up on the pan; the edges on larger tortillas might need support when the shells are inverted so loosely crumple some foil into 4-inch balls and push them against areas that sag.
Return the shells to the oven and bake until they're crisp, about 2 to 3 additional minutes.
Let cool on rack.
Repeat all steps until you have enough shell bowls for your meal.