Heat 1 Tbsp. oil in a large sauté pan over a high flame until hot. Add the and onions and season with a dash of salt. Shake the pan every few minutes until the onions have wilted and started to caramelize, about 20 minutes.
Preheat oven to 450 degrees. Place veggie burgers on a baking sheet. Bake in the oven for 4-5 minutes on each side.
Toast buns and assemble your burgers with a lettuce leaf, a tomato slice and your favorite burger accompaniments.