Preheat the oven to 425 degrees F. Line a baking sheet with foil and spray generously with the olive oil spray.
Split the focaccia horizontally and cut into 4 sandwich bread-size portions. Put the bottom of each sandwich cut-side up on the prepared baking sheet. To each piece of focaccia, add 1/3 cup each of the Cheddar, chicken, asparagus, potatoes and mozzarella, then top with 1 slice Gouda. Top with the remaining slices of focaccia.
Spray the tops of the bread generously with the olive oil spray and cover with a sheet of foil. Put a baking sheet on top and weigh it down with a cast-iron skillet. Bake until the cheese is melted and the bread is golden, about 20 minutes.
You can substitute raw spinach, cooked kale or even string beans for the asparagus.