Combine the lime juice, tequila, Cointreau and simple syrup in a pitcher. Stir well until combined.
Place a layer of salt on a small plate. Moisten the rim of a glass with a lime wedge and dip the glass in the salt. Wiggle the glass to cover the wet part of the rim completely. Repeat to rim the remaining glasses.
Fill the glasses with ice, then fill them halfway with the tequila-lime mixture. Top the glasses with the prosecco, garnish with lime slices and serve.
To make simple syrup, simmer equal parts sugar and water until the sugar is dissolved, then let cool.