Preheat oven to 375 degrees F (190 degrees C). Grease a baking sheet.
Pull the soft middle section out of each side of French bread and tear middle sections into pieces.
Stir Monterey Jack cheese cubes, sour cream, spinach, mushrooms, and seasoned salt together in a large bowl.
Melt butter in a large skillet over medium heat. Cook and stir garlic in hot butter until fragrant, 1 to 2 minutes. Stir bread pieces into garlic mixture; cook and stir until bread soaks up butter and begins to toast, 3 to 5 minutes. Remove from heat and add bread mixture to sour cream mixture; stir.
Stuff each bread crust with sour cream-spinach mixture and place loaves crust-side down on the prepared baking sheet.
Bake in the preheated oven until cheese is melted and tops begin to brown, about 30 minutes. Let sit for 10 minutes before slicing.