1. Preheat oven to 400 degrees F.
2. Mash all ingredients except oil together. Divide the mixture into four equal balls, and form each into a patty.
3. Heat oil in a medium, oven-proof skillet over high heat and cook the patties until lightly browned (1 minute per side).
4. Transfer skillet to oven and bake until firm (15 minutes). Serve patties on buns, topped with fresh veggies as desired.