Vegetarian Gefilte Fish

Name: Vegetarian Gefilte Fish
Ingredients: 42 grams (about 1 medium) carrot, half peeled and roughly chopped (scant 1/4 cup); half left whole; 75 grams (3/4 cup) roughly chopped cauliflower; 75 grams (about 1/4 medium, 3/4 cup) peeled roughly chopped parsnip; 33 grams (1/4 cup) raw, unsalted cashews or walnuts; 40 grams (1/4 medium, heaped 1/4 cup) white onion; 1 large egg; Kosher salt; 1/2 teaspoon freshly ground black pepper; 1/2 teaspoon granulated sugar; 1 1/2 teaspoons Old Bay Seasoning; 1 teaspoon very finely ground wakame powder; 1 large lemon; 2 tablespoons matzo meal (not matzo ball soup mix); Prepared horseradish, for serving; Roughly chopped parsley or dill, for garnish (optional)