1. Place oven rack 8 inches from broiler heat. Preheat broiler on high. Line a large rimmed baking pan with foil; place a wire rack in baking pan.  
2. Microwave butter in a 1-cup microwave-safe measuring cup on high 25 to 35 seconds or just until melted; cool slightly. Stir in lemongrass paste; mash lemongrass paste against side of measuring cup with the back of a metal spoon to release flavor. Whisk in lime zest and juice. Set butter mixture aside.  
3. Pat lobster tails dry with paper towels. Using kitchen scissors, cut through center of shells, stopping at base of tails. Turn lobster tails over and cut ribs down the center to base of tails. At base of cut, make a snip to the right and left; this will help you open the shells. Turn the lobster tails over and use your thumbs and fingers to spread shells open. Gently loosen the lobster meat from shells; lift and set lobster meat over top of shells. Remove black vein, if necessary. 
4. In prepared baking pan, place lobster tails, meat sides up. Top each with 1 tsp. butter mixture. Broil 5 to 7 minutes or until lobster meat is opaque and white, 145°F. 
5.  Heat and whisk remaining butter mixture. Stir in 1 tsp. cilantro. Brush over lobster meat. Garnish with cilantro. 

Each serving contains: 160 calories, 7 g fat, 4 g saturated fat, 0 g trans fat, 185 mg cholesterol, 650 mg sodium, 2 g carbohydrates, 0 g fiber, 0 g sugar, 22 g protein. Daily values: 0% vitamin D, 8% calcium, 0% iron, 6% potassium.