Preheat grill to medium-high heat. Remove lobster from shell.
Dice tomatoes, bell peppers, cilantro, and avocado. Slice radishes and cut limes into wedges. Wrap tortillas in foil and set everything aside.
Make chipotle ranch dressing if you are making homemade. Refrigerate until ready to use. This step can be done several hours or a day ahead of time.
Place tortillas on the top rack of the grill to heat, or place in toaster oven to heat the tortillas. You can also place them directly on the grill if you like them a little bit crunchier.
Cook lobster on the grill for 2 minutes. Turn and continue to cook for 2 more minutes, or until the lobster turns opaque and is done in the center. Remove from grill. Cut into bite-sized pieces.
To assemble tacos, place cabbage in the bottom of the tortilla. Add pieces of lobster to each taco and arrange tomatoes, bell peppers, cilantro, radishes and avocado on top. Sprinkle with grated cheese. Drizzle chipotle ranch over everything and garnish tacos with a wedge of lime and extra sauce.