Cook bacon in a large, deep skillet over medium-high heat until evenly browned, about 10 minutes. Drain on a paper towel-lined plate.

While the bacon is cooking, melt butter in a large skillet over medium heat. Add onion and cook, stirring occasionally, until soft and translucent, 7 to 10 minutes, adding garlic for the last minute. Stir in spinach and cook until wilted, about 3 minutes. Remove from the heat.

Preheat a panini press according to the manufacturer’s instructions.

Stir mayonnaise, chipotle peppers, and adobo sauce together in a small bowl. Spread mixture over 4 slices of focaccia bread, then top each slice with provolone, turkey, two slices bacon, spinach mixture, and remaining bread slices.

Cook sandwiches in the preheated panini press until crispy and golden brown, about 5 minutes each.