2 medium red beets
3 tablespoons olive oil
Kosher salt and freshly ground black pepper
2 medium sweet potatoes
2 medium russet potatoes
8 frozen breaded fish fillets, such as Gorton's
1/2 cup vegan or regular mayonnaise
1 tablespoon sweet relish
1 teaspoon yellow mustard
1 teaspoon lemon juice, plus lemon wedges, for serving
Chopped fresh parsley, for serving