In a large skillet over medium heat, add a splash of oil and sauté sliced mushrooms until they become tender and golden, about 4 minutes. Then, toss in minced garlic and diced red onion, stirring for an additional 2 minutes until fragrant. Remove the mixture from the heat and set it aside to cool slightly.

Wipe down the skillet and drizzle in a little more oil if needed, then increase the heat to medium-high. Add the diced bell peppers and sauté for 1 minute until just tender, then fold in the chopped baby spinach until wilted, which should take about 2 minutes. Set the vibrant mixture aside with the other cooked veggies.

Preheat your oven to 375°F (190°C) and spray a 9×13-inch baking dish with nonstick cooking spray. Press the thawed shredded potatoes evenly into the bottom of the dish, forming a solid base.

Spread the sautéed mushroom and onion mixture over the layer of hash browns. In a separate bowl, whisk together the eggs, half and half, hot sauce, salt, and pepper. Pour this creamy egg mixture evenly over the veggies.

Generously sprinkle the shredded cheese of your choice over the entire top surface of the casserole.

Place the casserole in the preheated oven and bake uncovered for 45-50 minutes. Allow the casserole to cool for about 10 minutes before cutting into squares.