Pat the chicken breast completely dry with a paper towel to ensure a proper sear, then season both sides thoroughly with the chili powder, cumin, sea salt, and black pepper.
Heat the olive oil in a heavy-bottomed skillet or cast-iron pan over medium-high heat until the oil begins to shimmer.
Carefully place the chicken in the hot pan and sear for approximately 5 to 7 minutes per side, allowing a deep, smoky char to develop while the meat remains juicy.
While the chicken is finishing, add the avocado, Greek yogurt, fresh spinach, unsweetened almond milk, and ice cubes into a high-speed blender.
Blend the smoothie ingredients on the highest setting for 45 seconds until the texture is perfectly velvety and the color is a vibrant, bright green.
Transfer the spicy charred chicken to a plate to rest for 2 minutes before slicing, then serve it immediately alongside the chilled, creamy smoothie for a nutrient-dense meal.