To prepare simple syrup, heat water and sugar on the stove, stirring until sugar is fully dissolved and mixture is at a boil. Remove from heat and add the jalapeño slices; letting it cool with the jalapeño infusing. Strain and discard the jalapeño when cooled and ready to use.
In a large pitcher, stir together orange juice, lime juice, tequila, and cooled simple syrup.
To create a sugar/salt rim, place 1/4 cup sugar and 1/4 cup kosher salt on a plate. Moisten the rim of four glasses with lime juice and carefully run the rim in the sugar/salt mixture.
Fill each glass with ice and pour margarita mixture evenly into each one. Serve with additional lime wedges and jalapeño slices if desired.