Combine tequila, lime juice, and Triple Sec in a tall glass or drink shaker. Add jalapeno slices and muddle well with a wooden spoon or rubber-tipped muddler, crushing the jalapenos to release their juice.

On a plate, combine salt, sugar, and chili powder.

Moisten the rim of your glasses with some lime juice (or the juice from a slice of jalapeno!) and dip the glass rim in the salt mixture. Fill the glass halfway with crushed ice, and pour the margarita mixture over the ice.

If desired, garnish the glass with a slice of jalapeno.