In a small mixing bowl, combine the Greek yogurt, minced chipotle peppers, garlic powder, sea salt, and black pepper to create a clean-ingredient chipotle aioli.
Lay the sourdough slices on a clean surface and spread the chipotle aioli evenly across one side of each slice.
On one slice of bread, layer the shredded chicken, fresh mozzarella, tomato slices, thinly sliced red onion, and fresh basil leaves.
Place the second slice of bread on top, sauce-side down, to close the sandwich.
Lightly brush the exterior of the sandwich with avocado oil to ensure a golden, crispy crust.
Heat a panini press or a heavy cast-iron skillet over medium heat.
Place the sandwich in the press or skillet; if using a skillet, place a heavy lid or another pan on top to press it down firmly.
Toast for 3 to 4 minutes per side until the bread is perfectly browned and the mozzarella has melted through.
Remove from heat, let it rest for one minute, then slice diagonally and serve warm.