Heat olive oil in a small saucepan over medium heat.
Add onion and cook until soft.
Add cascable and ancho powder and cook for 1 minute, let cool. Fold onion mixture into softened butter, add lime juice and season with salt and pepper to taste.
Place in a bowl and refrigerate until firm.
Preheat grill.
Brush lobster tails with oil and season with salt and pepper.
Place meat side down and grill 3 to 4 minutes on each side or until cooked through.