1. Preheat oven to 400 degrees. Prepare avocados by cutting in half, pitting, and sprinkle insides with lime juice; set aside in shallow baking dish.
2. In large heavy skillet, combine butter and onion, saute over medium-low heat just until onion becomes transparent.
3. Sprinkle flour into skillet with onions and whisk over medium-low heat for 2 minutes.
4. Drizzle in milk slowly, whisking constantly, until milk is incorporated and mixture becomes thick; remove skillet from heat.
5. In separate bowl, mix together crab meat, mustard, and Pickapeppa Sauce, then pour into skillet and stir together the two mixtures.
6. Spoon the mixture into the avocado indentation (where pit was) and sprinkle with Parmesan cheese.
7. Put in preheated oven and bake at 400 degrees for 13 to 15 minutes or until the avocados are just heated through.
8. No Pickapeppa sauce? Use any sweet, tangy sauce like vinaigrette, Worcestershire sauce, or steak sauce, or even a sweet barbeque sauce or salsa.