Slice the mushrooms and onion. Chop the tomato, shred the lettuce, and slice the pickles. In a small bowl, mix the Greek yogurt, light mayonnaise, and ketchup until smooth. Refrigerate the sauce.
Heat the olive oil in a large skillet over medium-high heat. Add the mushrooms and cook for 6–8 minutes, stirring occasionally, until browned and their released moisture has evaporated.
Add the onion and cook for another 4–5 minutes until softened and lightly golden. Transfer the vegetables to a plate.
Add the ground beef to the same skillet. Break it into crumbles and cook for approximately 6–8 minutes, until browned and it reaches 160°F (71°C).
Stir in the garlic powder, onion powder, smoked paprika, salt, black pepper, Worcestershire sauce, and mustard.
Return the mushrooms and onions to the skillet. Stir and cook for 1–2 minutes until everything is combined.
Divide the beef mixture into four equal portions. Top each with one slice of Swiss cheese, cover briefly over low heat, and allow the cheese to melt.
Divide the lettuce between four bowls. Add the warm beef mixture, tomato, and pickles. Drizzle with the prepared sauce and serve.