Melt the butter in a small pot over low heat. Remove from the heat and stir in the chili powder, garlic powder, cayenne pepper, black pepper, and lemon juice. In a measuring cup whisk together the vegetable juice and corn starch. Add the broth mixture to the butter mixture and whisk for one minute. Fold in the flaked crab meat, mix well, then divide the mixture between two serving size casserole dishes and place on a baking sheet. Sprinkle with sliced scallions and Parmesan cheese.