Prepare a tall stockpot for steaming by filling with 2 inches of water. Add vinegar, and fit stockpot with a steamer basket; bring to a boil over high. Add lobsters, in batches if necessary; cover and steam 12 minutes. Submerge lobsters in an ice bath, and let stand until completely cooled, 5 to 10 minutes.
Carefully remove meat from tail, claws, and knuckles. Slice the meat into bite-size pieces, and set aside.
Place butter, chili powder, lime zest, lime juice, and shallots in a large skillet; cook over medium until butter is completely melted, 2 to 3 minutes. Remove from heat; add lobster, and gently stir until lobster is heated through. Using a slotted spoon, remove lobster from skillet, and place about 3 to 4 tablespoons of the lobster in each warm tortilla. Top with desired amount of butter mixture, and sprinkle evenly with the scallions and parsley. Serve immediately.