Place the chopped Yukon Gold potatoes and 1 teaspoon salt in a pot. Cover with cold water, bring to a boil, then reduce heat to medium and cook until fork tender, about 20 to 25 minutes. Drain and return to pot.

Add milk, butter, garlic powder, remaining salt, and black pepper to the drained potatoes. Use a potato masher to achieve a creamy consistency, ensuring there are no lumps.

In a skillet over medium heat, pour in olive oil and sauté the finely chopped onion for about 10 minutes until soft and translucent. Stir in ground beef and mushrooms, cooking until browned and tender, about 8 to 10 minutes. Season with 7 Spice and remaining salt.

Preheat your oven to 350°F (175°C). Spray a baking dish with olive oil cooking spray to prevent sticking.

Spread half of the creamy mashed potatoes across the bottom of the dish. Layer the cooked beef filling over the mashed potatoes, then top with the remaining mashed potatoes.

Evenly sprinkle the panko breadcrumbs on top and lightly spray with olive oil. Bake uncovered for about 30 to 35 minutes, until golden brown.

Allow the souffle to cool for 10 minutes before cutting into 12 squares and serving warm, enjoying the delightful layers.