To prepare relish: Remove the peel and white pith from grapefruit with a sharp knife and discard. Cut the grapefruit segments from the surrounding membrane, letting them drop into a small bowl. Squeeze out remaining juice into the bowl and discard membrane. Add avocado, shallot, cilantro, vinegar and honey. Toss well to combine.
To prepare turkey: Combine chili powder, five-spice powder and salt on a plate. Dredge turkey in the spice mixture.
Heat oil in a medium skillet over medium-high heat. Add the turkey and cook until no longer pink in the middle, about 2 to 3 minutes per side. Serve the turkey with the avocado-grapefruit relish.
Note: Often a blend of cinnamon, cloves, fennel seed, star anise and Szechuan peppercorns, five-spice powder was originally considered a cure-all miracle blend encompassing the five elements (sour, bitter, sweet, pungent, salty). Look for it in the supermarket spice section.