Use a heavy sharp knife to cut the lobster tails in half. (Place your knife on the end where the flesh is exposed and cut down through to the tail.)
Brush the exposed flesh with oil and season with salt and pepper. Reserve.
In a small pan, over medium heat, melt butter. When it starts to bubble, add garlic, half of the cilantro, jalapeno, citrus zest and 1 tablespoon lemon juice. Stir for 1 minute, then remove from heat and reserve.
Half and pit avocados. In a medium bowl, mash avocado with 2 tablespoons lemon juice, the remaining cilantro and the green onion. Season to taste with salt and pepper. Reserve.
Preheat grill to medium/medium-high direct heat, or heat a heavy skillet to medium-high.
Place lobster tails cut-side down on grill or pan and cook for 4 minutes. Flip, and baste generously with butter mixture. Cook for 2 more minutes, or until tails are cooked throughout.
As the tails are cooking, burnish the tortillas on the grill or stovetop until toasted.
Spread avocado mixture and salsa over each of the tortillas, then place lobster tails, in their shells, overtop. Instruct the diners to pull their own lobster meat.