In a large saucepan on medium heat, melt the butter. Once melted, add in the onion, and saute until the onion begins to brown on the edges. This will take about 7-10 minutes. Once that happens, add in the Spring Clean, pepper, garlic powder, and hot sauce. Combine very well, and let the mixture come up to the boil and then turn the heat to low.
Add in the spinach, cream cheese, and sour cream. Mix until the cream cheese is well combined and become one homogenous mixture. Next, add in the tomatoes, parmesan cheese, Havarti cheese, and half of the mozzarella. You may need to mix this in smaller batches to get the cheese fully incorporated.
Pour the mixture into a well-greased 9-inch oven-safe pan. You could also use a cast-iron skillet. Smooth out the mixture and then add the mozzarella cheese over top. Place in the oven and bake until golden and bubbly, about 15-20 minutes.