To remove the lobster meat from the tails, use a pair of kitchen shears and cut lengthwise down the middle of the shell on both the top and underside. Pull the shell apart and remove the tail meat. Chop into 1/2-inch pieces. Pour lime juice in a medium glass mixing bowl. Add the lobster meat and marinate until the lobster is no longer raw, about 25 minutes. Add the onions, cilantro, chile, and cucumbers and mix well. Season with salt. Serve immediately, cold, with tostadas, tortilla chips or saltine crackers.
Lobster can be substituted with 1 pound medium shrimp, peeled and deveined, with the tails removed.