Preheat the grill to medium heat.
Melt butter in a small saucepan over low heat, then stir in garlic and chili powder until well combined. Remove from heat once fragrant (avoid burning). Stir frequently while cooking.
Peel back the husk of each ear of corn to expose its kernels.
Brush or dip ears into butter mixture, ensuring even coverage on all surfaces and in between individual rows of kernels. Sprinkle lightly with lime zest if desired.
Place directly onto the grill over medium heat for about 15-20 minutes until corn is tender to bite and slightly charred.
Allow ears to cool briefly before serving, either off of the cob or back inside their husks with butter mixture still attached.