Start by soaking the minced onion in the lime juice. Sprinkle salt over it and mix well. Now cut all your other vegetables. Doing it this way will take the sting out of the onions.
Chop all your other vegetables and add them to the bowl with the lime juice and onions. Mix well and add salt to taste. Have this ready for the lobster.
Heat your tortillas now. If you are making your own, make them after the salpicon but before you steam the lobster.
Set a steamer tray in a pot and pour enough water to come up to just below the level of the tray. Cover the pot and bring this to a boil. Lift the lid, set the lobster tails on the tray, cover the pot and steam for about 10 to 15 minutes. Big Maine lobster tails can take 15 minutes, but little Caribbean or Pacific lobster tails will only take about 10 minutes.
Meanwhile, melt the butter in a little pot. When the lobster is ready, remove it from the shells and cut into bite-sized pieces. Put the lobster in a bowl and toss with the melted butter.
Mix the lobster with the salpicon, add it to tortillas and have at it!
NOTE: This makes a zippy taco. If you want things less spicy, tone down the peppers. Maybe go with one habanero, or downgrade to serranos. If you are really not into heat, use supermarket jalapenos, which are typically not very hot.