Preheat an outdoor grill for medium-high heat and lightly oil the grate.

Combine turkey, red onion, sour cream, mustard, and steak seasoning in a bowl until well mixed. Form into four 3/4-inch thick patties. Drizzle with olive oil on both sides and season with salt.

Cook on the preheated grill until cooked through, about 5 minutes per side, laying Swiss cheese over burgers just before removing from the grill. An instant-read thermometer inserted into the center of the burgers should read at least 165 degrees F (74 degrees C).

Place burgers on buns and serve.