It's generally best to season meat *before* freezing. This allows the flavors to penetrate the meat during the freezing and thawing process, resulting in a more flavorful final product.
Seasoning meat before freezing offers several advantages. First, the salt in the seasoning helps to draw out moisture, which can then refreeze and create ice crystals. While some ice crystal formation is inevitable, reducing moisture content can minimize freezer burn. Second, the spices and herbs have more time to infuse the meat, leading to a deeper and more even distribution of flavor. When you freeze unseasoned meat, you miss this opportunity for flavor enhancement during the extended storage period. When thawing, the meat will absorb the seasoning more effectively than if you were to season it right before cooking. Consider using a generous amount of seasoning, as some flavor intensity may be lost during the freezing and thawing process.
Avoid using garlic or onion powder in your pre-freezing seasoning mix. These spices can sometimes develop an off-flavor during long-term freezing. Instead, add fresh garlic or onion when you cook the meat after thawing for the best flavor.